Tomato, Squash, and Bell Pepper Gratin

As an Amazon Associate, I earn from qualifying purchases. Read the full disclosure here.

Grab those late summer vegetables and make a flavorful vegetable gratin side dish with vegetables, cheese, and a breadcrumb topping.

A baking dish full of vegetables including tomatoes and squash.

This is the first week that I haven’t been able to go and get our CSA.   I’m back to work so my husband has to go get it on Fridays.

I really miss not being able to pick it up and then go to the farmer’s market.  I’m lucky enough that my husband can still go and I can send him with a list of things I’m looking for.

what is a csa?

CSA stands for “Community Supported Agriculture.” It is a collaborative model of food production  that connects local farmers directly with consumers.   It provides mutual benefits for both parties as the CSA members purchase shares from a local farm and then receive a portion of the farm’s produce on a regular basis throughout the season.  The farmer in turn receives money to help fund their farm.

This week we received 2 heads of lettuce, the biggest cabbage you’ve ever seen, 2 huge tomatoes, a large bunch of basil, 3 onions, 5 garlic cloves, and 3 yellow squash.  Not the biggest bunch we’ve had, but things we will use.

I decided to use the tomatoes and squash in a vegetable side dish.   Side dishes are probably the hardest thing for me to decide on when I’m cooking.  I looked through a lot of different dishes before I settling on this vegetable gratin.


  • olive oil
  • onions (I prefer sweet onions but use your favorite type)
  • bell pepper (any color)
  • yellow squash
  • garlic cloves
  • salt and pepper
  • milk (you can substitute plant based milk but stir in 2 tablespoons of flour to the milk)
  • mozzarella cheese (shredded)
  • egg
  • tomatoes (large tomatoes work best but you can substitute cherry tomatoes)
  • panko breadcrumbs

The longest part of the prep for this dish is all the cutting.  The onions and the bell pepper need to be thinly sliced so that they will cook in the oven.

The yellow squash is cut in half lengthwise and then cut into half moons.  The tomatoes are cut into thin slices.

A cutting board with ingredients for Tomato Gratin on it.

Can I substitute the yellow squash?

You can substitute other easy to cook squash in this recipe in place of the yellow squash.  Good choices would include eggplant, zucchini, or delicata squash.

Can I use other tomatoes?

You can use cherry tomatoes in this recipe.   The tomatoes add liquid and flavor to the dish so make sure you use them.  The first few times I made this I used large tomatoes which added a ton of flavor but were hard to cut in the vegetable gratin.   I switched to cherry tomatoes this time and it was much easier to eat but did not add quite as much flavor.

The vegetables need to be sauteed on the stove top for a few minutes before going into the baking dish.  This helps soften them so they cook more easily in the oven.

Then the onions, bell peppers, and squash are placed in the baking dish.  A quick sauce of milk, cheese, and egg is poured over top of the vegetables in the dish.

Finally the tomatoes are placed on top of the mixture.   Breadcrumbs are sprinkled over top of the tomato gratin right before baking.

how do I store this dish?

This vegetable side dish is best eaten on the day it is made.  If you are going to store it put it in an air tight container in the refrigerator for up to 2 days.  When ready to reheat you can put it in the microwave but the cheese tends to be clumpy.  I recommend putting it in the oven, covered, at 350 until it is heated through.

This is one of the best vegetable side dishes I’ve had in a while and it made great use of the tomatoes, squash, garlic, and onions I received in my CAS.

A baking dish full of vegetables with breadcrumbs on top.

I don’t even like tomatoes on their own but these homegrown beauties were amazing. They added a ton of big flavor to the dish which was delicious.

More vegetable side dishes:

I mixed the vegetables with some milk, egg, and cheese and it made a delicious, fresh tasting casserole.  This really is a great dish to serve in the summer because it uses all that beautiful fresh produce you can grow yourself or buy at the local farmer’s market.

You can also substitute in different vegetables you have on hand to make it your own.  Other vegetables that would work in this dish would be zucchini, butternut squash, sweet potatoes, or regular potatoes.

Pin Image:   Text title, a plate with a piece of chicken and a scoop of tomato gratin.

If you’ve tried my Yellow Squash, Bell Pepper, and Tomato Gratin or any other recipe on Hezzi-D’s Books and Cooks please take a minute to rate the recipe and leave a comment letting me know how you liked it. I love hearing from you! You can FOLLOW ME on:

Pin Image: Text title, a plate with a piece of chicken and a scoop of tomato gratin.

Tomato, Squash, and Bell Pepper Gratin

5 from 16 votes
Print Pin
Prep Time: 10 minutes
Cook Time: 30 minutes
Total Time: 40 minutes
Author: Hezzi-D


  • 1 Tablespoon olive oil
  • 1 onion thinly sliced
  • 1 green bell pepper thinly sliced
  • 1 yellow squash cut in half lenthwise then sliced
  • 3 garlic cloves minced
  • 1 teaspoon salt
  • 1 teaspoon black pepper
  • 1/4 c. low fat milk
  • 1/4 c. mozzarella cheese
  • 1 egg
  • 1 large tomato cut into thin slices
  • 1/3 c. panko breadcrumbs


  • Preheat the oven to 375 degrees.
  • Heat the oil in a skillet over medium heat. Add the onions, peppers, squash, and garlic. Sprinkle with salt and pepper. Saute for 5 minutes or until just beginning to soften.
  • Place the softened vegetables in a 9" square baking pan.
  • In a small bowl combine the milk, mozzarella cheese, and egg. Mix well and pour over top of the vegetables.
  • Place the tomato slices on top of the vegetables. Sprinkle with the panko breadcrumbs.
  • Bake for 25-30 minutes or until the breadcrumbs have browned.


Source: Adapted from My Recipes

A plate with a piece of garlic parmesan chicken and a serving of Toato Gratin.
5 from 16 votes (16 ratings without comment)

Leave a Reply

Your email address will not be published. Required fields are marked *

Recipe Rating