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Summer Squash Tomato Gratin

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This delicious yellow squash and tomato gratin is easy to make and results in a wonderful side dish with a crispy, cheesy topping.

You can use summer squash or zucchini for this recipe, along with tomatoes, bell pepper, and shallots.

This recipe serves 6 as a side dish, but I love to eat it as a main course as well!

A closeup shot of squash tomato gratin in a baking dish with a silver spoon.

Why You'll Love Tomato Squash Casserole

This delicious squash, tomato, and bell pepper dish is bursting with summer flavors and makes for a delicious side dish or lighter main course!

The panko and cheese toast nicely and combine to create a savory crust for the vegetables.

This recipe is a great dish to take to a potluck or picnic.

Ingredients for a summer squash, tomato, and bell pepper gratin.

Ingredients You'll Need

Summer Squash - You'll need two yellow squash (also called straight neck squash, or yellow zucchini) for this recipe. If you'd prefer, you can also use two zucchini squash.

Tomatoes - You'll need three medium or two large tomatoes. I used heirloom tomatoes because I love their flavor, but you can also use beefsteak, Roma, or any other tomato type you have on hand.

Bell Pepper - You'll need one bell pepper for this recipe. I used an orange bell pepper (for the taste and color), but you can also use orange or yellow. I would not recommend using a green bell pepper.

Shallots - You'll need two medium-sized shallots for this recipe. If you can't find shallots, you can also use half a red onion.

Gruyere - You'll need 1 cup of shredded gruyere cheese.

Panko - You'll need ½ cup of Panko breadcrumbs for this recipe. You can use regular breadcrumbs, but I find them denser and less easy to crisp.

Seasonings - You'll need 1 teaspoon of Italian seasoning for this recipe. Make your own blend using our Italian seasoning recipe. You'll also need 1 teaspoon of kosher salt and ½ teaspoon ground black pepper.

Four photos showing how to layer the gratin.

Tips for Choosing the Best Produce

When choosing the best summer squash, you'll want to look for size, firmness, and blemish-free skin. Squash that have grown too large will be lacking in flavor and will have a dry texture. Squash should have a firm texture with no bruising and skin that isn't pockmarked.

The best tomatoes will be firm and heavy for their size. They shouldn't have any bruises, holes, or tears. Great tomatoes will also smell very aromatic!

Finally, the best bell peppers will be brightly colored, firm, and without any visible bruising or marks.

An overhead shot of a tomato squash gratin.

More Summer Side Dish Recipes to Try

Try some of our other seasonal favorites that feature tomatoes, squash, and bell peppers.

Tips for Making this Recipe

Cooking Tips - If your panko is not browning, but the vegetables are roasted, turn on your broiler for one or two minutes to crisp the topping.

Specialty Ingredients - This recipe calls for Italian seasoning. You can make your own blend with our Italian seasoning recipe.

Recommended Tools - You'll need a large baking dish (9x13 or similar sized) for this recipe. Here's the one I use.

Storing Tips - You can save this dish in the refrigerator for up to 4 days, but I think it's best the day you make it (the topping is crispier straight out of the oven). I would highly recommend you reheat it in the oven.

If you try this recipe, let us know! Connect with us on Instagram and share your photos or leave us a rating.

Yield: 6 servings

Summer Squash Tomato Gratin

A closeup shot of squash tomato gratin in a baking dish with a silver spoon.

This easy summer squash, tomato, and bell pepper gratin is a wonderful, fresh side dish.

Prep Time 10 minutes
Cook Time 25 minutes
Total Time 35 minutes


  • 2 yellow squash, sliced into coins
  • 2 large or 3 medium heirloom tomatoes, sliced
  • 2 shallots, thinly sliced
  • 1 orange bell pepper, diced
  • 1 teaspoon kosher salt
  • ½ teaspoon ground black pepper
  • 1 teaspoon Italian seasoning
  • 1 cup shredded gruyere cheese
  • ½ cup panko breadcrumbs


  1. Preheat oven to 400 degrees F.
  2. Arrange the sliced summer squash along the bottom of a 9x13 baking dish.
  3. Sprinkle with a little of the salt, pepper, and Italian seasoning. Then sprinkle with a small amount of the panko breadcrumbs and shredded gruyere.
  4. Layer the tomatoes on top of the squash. Repeat with sprinkling on the salt, pepper, Italian seasoning, breadcrumbs, and cheese.
  5. Sprinkle the bell pepper and shallots in a layer across the tomatoes.
  6. Top the dish with the remaining salt, pepper, Italian seasoning, breadcrumbs, and cheese.
  7. Bake for 25 minutes or until the panko is golden brown.
  8. Serve immediately or save in the refrigerator for up to 3 days.

Nutrition Information:



Serving Size:


Amount Per Serving: Calories: 182Total Fat: 9gSaturated Fat: 5gTrans Fat: 0gUnsaturated Fat: 3gCholesterol: 25mgSodium: 447mgCarbohydrates: 18gFiber: 4gSugar: 7gProtein: 10g


Sunday 30th of June 2024

I halved the recipe and added a top layer of squash as I had one more to use.


Tuesday 2nd of July 2024

Sounds perfect!


Sunday 30th of June 2024

This turned out yummy. I haves as I am cooking for two.


Tuesday 20th of September 2022

I made this dish as a side for lunch. It turned out fantastic. We have a lot of cherry tomatoes from our yard and those worked great in this dish. I used Asiago as that was the cheese that I had. After 25 minutes it wasn't done though it was browned on top. I covered it with foil and reduced temperature to 350F. It was in there for another 15 minutes and at that point it was just perfect. Thx so much for a great recipe!

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