f your garden or your fridge is bursting with zucchini and yellow squash, this is the recipe you need on repeat. It’s my version of a summer squash ratatouille, not the stovetop kind that simmers forever, but an oven-baked, hands-off dish that’s as delicious as it is beautiful.

We’re talking thin layers of zucchini, yellow squash, juicy tomatoes, and sweet onions, all seasoned with garlic and herbs and topped with a layer of melty cheese. It’s the kind of side dish that steals the spotlight at summer dinners and it also happens to be naturally gluten-free and veggie-packed.
If you love vibrant veggie recipes like my Sheet Pan Gnocchi with Veggies and Sausage or my Tuscan Bean Salad, you’ll definitely want to add this one to your summer rotation.
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The ingredients
You will need these simple ingredients you can easily find at your grocery store to make this roasted zucchini and summer squash casserole.
Notes on the ingredients
Zucchini – Thinly sliced for layering; choose small to medium for best texture
Yellow squash – Adds color and sweetness
Roma tomatoes – Sliced; they roast down into juicy bursts
Red onion – Adds a bit of bite and richness
Garlic – Freshly minced for maximum flavor
Olive oil – For drizzling and roasting
Italian seasoning – A simple blend that complements all the veggies
Salt and pepper – Always to taste
Shredded Cheddar – Optional, but makes it melty and irresistible
For quantities see recipe card below
How to make the Summer Squash Ratatouille
- Preheat and prep – Preheat the oven to 375°F and lightly grease a baking dish.
- Layer the veggies – Arrange the zucchini, yellow squash, tomatoes, and onions in overlapping layers. Alternate colors to make it visually appealing.
- Season – Sprinkle the veggies with minced garlic, Italian seasoning, salt, and pepper. Drizzle with olive oil.
- Bake uncovered – Bake for 30–35 minutes until the vegetables are tender and slightly caramelized on the edges.
- Add cheese – Sprinkle shredded cheese over the top and bake for another 5–10 minutes until melted and golden.
- Serve – Let it cool slightly, then serve warm as a side or even a light main with crusty bread or quinoa
Tips
Here are some helpful tips to ensure your roasted zucchini and summer squash casserole turns out perfectly:
- Try to slice the zucchini, yellow squash, tomatoes, and onions into uniform ¼-inch rounds. This helps in even cooking and ensures all the vegetables have a consistent texture.
- Choose fresh vegetables for the best flavor and texture. Farmers' markets are great places to find high-quality produce during the summer months.
- When layering the vegetables in the baking dish, consider arranging them in an overlapping pattern. This not only looks beautiful but also helps the flavors to mingle during baking.
- Keep an eye on the casserole while it's baking. The baking time may vary depending on your oven's temperature and the thickness of the vegetables. You want the vegetables to be tender but not mushy.
Variations
- Add some crumbled feta cheese, and a sprinkle of dried Italian seasoning to the casserole for a Mediterranean flair. The tangy feta complement the roasted vegetables beautifully.
- Add sliced ham or turkey between the veggies slices for a complete meal
- Instead of just adding cheese on top, create layers of cheese between the vegetable slices. Try mozzarella, provolone, or fontina to make the casserole ooey-gooey and even more flavorful.
Serving
- Pair it with: grilled chicken, tofu, rice, or crusty bread
- Leftovers: Store in the fridge up to 4 days
- To reheat: Use the oven for best texture, or microwave if you're in a hurry
FAQ's
If you’re a perfectionist and want all the veggies to have a uniform look, try using a mandolin to get the same diameter for each slice. Ideally, each slice should be about ¼ inch in diameter.
While the recipe calls for cheddar and parmesan cheese, feel free to experiment with other cheese varieties like mozzarella, gruyere, or feta for unique flavor profiles.
Mediterranean Flavors
Summer Squash Ratatouille (Easy Baked Zucchini Casserole)
Equipment
- 9x9 or similar size baking dish
- Sharp knife or mandoline
- Cutting board
- Measuring spoons
Ingredients
- 1 large zucchinis sliced into ¼ inch rounds
- 1 larges yellow squash sliced into ¼ inch rounds
- 3 to 5 Italian tomatoes hulled, seeded, sliced into ¼ inch
- 2 red onion sliced into ¼ inch
- ¼ cup olive oil
- 1 teaspoon onion powder
- 1 teaspoon garlic powder
- Salt and pepper from the mill
- ½ cup cheddar cheese grated
- ¼ cup parmesan grated
Instructions
- Begin by preheating your oven to 375°F (190°C). Grease a medium-sized baking dish lightly with olive oil to ensure your casserole doesn't stick.
- Wash and slice the zucchini, yellow squash, Italian tomatoes, and red onions into uniform ¼-inch rounds. The even thickness ensures even cooking.
- Take your vegetables and layer them in the prepared baking dish, alternating between zucchini, yellow squash, tomatoes, and red onions. The combination of colors will create a visually appealing presentation.
- After 20 minutes sprinkle the grated cheddar and parmesan cheeses over the top. Pop the dish back into the oven for an additional 10 minutes, or until the cheese is melted and golden brown.
- Once your roasted zucchini and summer squash is cooked to perfection, take it out of the oven and let it cool slightly. Serve it as a side dish to complement your main course
Notes
- Use leftover roasted veggies in grain bowls or wraps
- Add a handful of fresh basil or parsley before serving
- Turn it into a main dish by adding white beans or cooked quinoa to the layers
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