Cheesy Summer Squash and Zucchini Casserole

Cheesy Summer Squash and Zucchini Casserole tastes like creamy mac and cheese met late-summer veggies and decided to settle down in a bubbly, golden baking dish. It works perfectly for busy weeknights or casual gatherings, and you can get it on the table in about 50 minutes, start to finish. I first made a version of this when my neighbor dropped off a mountain of zucchini, and my kids asked if we could have it again the next night.

Why Choose This Cheesy Summer Squash and Zucchini Casserole

This casserole turns simple summer squash and zucchini into a cheesy, comforting side that feels cozy but still tastes fresh. The vegetables soften in the oven, soak up garlic and herbs, and hide under a blanket of melty cheese that browns beautifully on top.

You can serve it with grilled chicken, pasta, or a big salad, so it fits into almost any dinner plan. It also uses basic pantry ingredients, so you avoid a long grocery list and still get a dish that tastes restaurant-level.

My whole family devoured this Cheesy Summer Squash and Zucchini Casserole and fought over the crispy edges. ★★★★★

Ingredients You’ll Need

Fresh produce

• 2 medium yellow summer squash, thinly sliced into rounds
• 2 medium zucchini, thinly sliced into rounds
• 1 small yellow onion, thinly sliced (or 1 teaspoon onion powder as a shortcut)
• 3 cloves garlic, minced (or 1 teaspoon garlic powder in a pinch)
• 2 tablespoons fresh parsley, chopped (or 1 teaspoon dried parsley)
• Optional: 1 teaspoon fresh thyme leaves or 1/2 teaspoon dried thyme

Dairy and eggs

• 1 1/2 cups shredded sharp cheddar cheese
  • I like extra sharp cheddar for stronger flavor; pre-shredded works, but block cheese melts smoother.
• 1 cup shredded mozzarella cheese
  • Any low moisture mozzarella works; store brand tastes fine here.
• 1/4 cup grated Parmesan cheese
  • Use the real stuff if possible; the green can works in a pinch but tastes a bit saltier.
• 1 cup whole milk or half-and-half
• 2 large eggs

Pantry items

• 3 tablespoons olive oil or melted butter
• 1/2 cup panko breadcrumbs or regular breadcrumbs
• 2 tablespoons all purpose flour
• 1/2 teaspoon kosher salt, plus more to taste
• 1/2 teaspoon black pepper
• 1/2 teaspoon smoked paprika or sweet paprika
• Optional: 1/4 teaspoon red pepper flakes for a little heat

Equipment

• 9×13 inch baking dish or similar casserole dish
• Large skillet
• Large mixing bowl
• Whisk
• Cutting board and sharp knife or mandoline slicer
• Measuring cups and spoons
• Aluminum foil

Tips & Tricks

• Slice the squash and zucchini evenly so they cook at the same rate; a mandoline on medium setting helps a lot.
• Salt the sliced vegetables lightly and let them sit 10 minutes, then pat dry, to reduce extra moisture and avoid a watery casserole.
• Use a mix of sharp cheddar and mozzarella so you get both strong flavor and great stretch.
• Pre cook the onion and garlic in a skillet until they soften and turn fragrant to build deeper flavor.
• Keep the milk at room temperature before you mix it with eggs so the custard bakes evenly.
• Cover the casserole with foil for the first part of baking so the veggies soften, then uncover to brown the cheese.
• If the top browns too quickly, tent loosely with foil and move the dish to a lower oven rack.
• Let the casserole rest 10 to 15 minutes before serving so it sets and slices more neatly.

How to Make Cheesy Summer Squash and Zucchini Casserole

Prep the vegetables

1. Preheat your oven to 375°F and grease a 9×13 inch baking dish with olive oil or butter.
2. Wash the summer squash and zucchini, trim the ends, and slice them into thin rounds about 1/8 to 1/4 inch thick.
3. Place the slices in a large bowl, sprinkle with a light pinch of salt, toss, and let them sit for about 10 minutes to draw out some moisture.
4. After 10 minutes, pat the slices dry with paper towels and set them aside.

Cook the aromatics

1. Heat 1 tablespoon olive oil in a large skillet over medium heat.
2. Add the sliced onion and cook 5 to 7 minutes until it turns soft and lightly golden.
3. Stir in the minced garlic and cook 30 to 60 seconds until it smells fragrant.
4. Remove the skillet from the heat and let the mixture cool slightly.

Mix the cheesy custard

1. In a large mixing bowl, whisk the eggs until they look smooth.
2. Add the milk or half-and-half, salt, black pepper, paprika, and red pepper flakes if you use them, then whisk again.
3. Stir in the cooked onion and garlic, parsley, and thyme.
4. Add 1 cup shredded cheddar, 1/2 cup shredded mozzarella, and the Parmesan, then stir until the cheese distributes evenly.

Assemble the casserole

1. Add the sliced squash and zucchini to the bowl with the cheesy mixture and toss gently to coat every slice.
2. Transfer everything to the greased baking dish and spread it into an even layer, tucking in any slices that stick up.
3. In a small bowl, mix the remaining 1/2 cup cheddar, 1/2 cup mozzarella, panko breadcrumbs, and 2 tablespoons olive oil or melted butter until the crumbs look evenly coated.
4. Sprinkle this cheesy breadcrumb mixture evenly over the top of the vegetables.

Bake to bubbly perfection

1. Cover the baking dish loosely with foil, place it on the middle rack, and bake for 20 minutes.
2. Remove the foil and bake another 15 to 20 minutes until the top turns golden and the casserole bubbles around the edges.
3. If you want extra crisp topping, switch the oven to broil for 1 to 2 minutes and watch closely so it does not burn.
4. Take the casserole out of the oven and let it rest 10 to 15 minutes before serving so the cheesy layers settle.

What to Serve with Cheesy Summer Squash and Zucchini Casserole

This Cheesy Summer Squash and Zucchini Casserole pairs nicely with simple grilled chicken, baked salmon, or roasted pork tenderloin. You can also serve it with a big green salad and crusty bread for a lighter, mostly veggie dinner. It tastes great next to turkey or ham, so it fits into holiday spreads as well. For a kid friendly plate, add some roasted potatoes or buttered noodles and call it a feast.

Storage Options

• Store leftovers in an airtight container in the fridge for up to 4 days.
• Reheat single portions in the microwave in 30 second bursts until hot, or use a 350°F oven for 10 to 15 minutes for best texture.
• To freeze, cool the casserole completely, wrap tightly, and freeze up to 2 months.
• Reheat from frozen in a 350°F oven, covered with foil, for about 30 to 40 minutes, then uncover for the last 5 to 10 minutes to crisp the top.

Cheesy Summer Squash and Zucchini Casserole

Cheesy Summer Squash and Zucchini Casserole is a creamy, veggie-packed side dish that bakes into a bubbly, golden casserole, perfect for busy weeknights or casual gatherings.

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Prep Time 20 minutes mins

Cook Time 30 minutes mins

Total Time 50 minutes mins

Servings: 8

Course: Drinner

Cuisine: American

Ingredients

  

• 2 medium yellow summer squash, thinly sliced into rounds
• 2 medium zucchini, thinly sliced into rounds
• 1 small yellow onion, thinly sliced
• 3 cloves garlic, minced
• 2 tablespoons fresh parsley, chopped
• 1 teaspoon fresh thyme leaves
• 1 1/2 cups shredded sharp cheddar cheese, divided
• 1 cup shredded mozzarella cheese, divided
• 1/4 cup grated Parmesan cheese
• 1 cup whole milk or half-and-half
• 2 large eggs
• 3 tablespoons olive oil or melted butter, divided
• 1/2 cup panko breadcrumbs or regular breadcrumbs
• 2 tablespoons all-purpose flour
• 1/2 teaspoon kosher salt, plus more to taste
• 1/2 teaspoon black pepper
• 1/2 teaspoon smoked paprika or sweet paprika
• 1/4 teaspoon red pepper flakes

Instructions

 

1. Preheat your oven to 375°F (190°C) and grease a 9x13 inch baking dish with olive oil or butter.
2. Wash the summer squash and zucchini, trim the ends, and slice them into thin rounds about 1/8 to 1/4 inch thick.
3. Place the slices in a large bowl, sprinkle with a light pinch of salt, toss, and let them sit for about 10 minutes to draw out some moisture.
4. After 10 minutes, pat the slices dry with paper towels and set them aside.

1. Heat 1 tablespoon olive oil in a large skillet over medium heat.
2. Add the sliced onion and cook 5 to 7 minutes until it turns soft and lightly golden.
3. Stir in the minced garlic and cook 30 to 60 seconds until fragrant.
4. Remove the skillet from the heat and let the mixture cool slightly.

1. In a large mixing bowl, whisk the eggs until smooth.
2. Add the milk or half-and-half, salt, black pepper, paprika, and red pepper flakes if using, then whisk again.
3. Stir in the cooked onion and garlic, parsley, and thyme if using.
4. Add 1 cup shredded cheddar, 1/2 cup shredded mozzarella, and the Parmesan, then stir until the cheese is evenly distributed.

1. Add the sliced squash and zucchini to the bowl with the cheesy mixture and toss gently to coat every slice.
2. Transfer everything to the greased baking dish and spread it into an even layer, tucking in any slices that stick up.
3. In a small bowl, mix the remaining 1/2 cup cheddar, 1/2 cup mozzarella, panko breadcrumbs, and remaining 2 tablespoons olive oil or melted butter until the crumbs look evenly coated.
4. Sprinkle this cheesy breadcrumb mixture evenly over the top of the vegetables.

1. Cover the baking dish loosely with foil, place it on the middle rack, and bake for 20 minutes.
2. Remove the foil and bake another 15 to 20 minutes until the top turns golden and the casserole bubbles around the edges.
3. For an extra crisp topping, switch the oven to broil for 1 to 2 minutes, watching closely so it does not burn.
4. Remove the casserole from the oven and let it rest 10 to 15 minutes before serving so the cheesy layers settle.

Notes

Nutrition Information
Approximate per serving (8 servings): 260–320 calories; fat 19–23 g; saturated fat 9–11 g; carbohydrates 13–17 g; fiber 2–3 g; sugars 5–7 g; protein 11–14 g; sodium 420–580 mg. Values will vary based on specific ingredients, brands, and portion size.