Skip to Content

Posh Squash (The Yummiest Zucchini and Yellow Squash Casserole)

Posh Squash is a delicious take on a traditional zucchini and yellow squash casserole. With a creamy egg filling and cheesy top, your family will want seconds and thirds of this side dish.

Zucchini and yellow squash casserole on a table.

My husband’s grandma sure knows how to cook.

She has some of the most amazing recipes and Posh Squash is one of them.

It’s the perfect way to use all of your garden zucchini and yellow squash.

How to Make Posh Squash – Step by Step

COOK 2 lbs zucchini and summer squash, sliced 1/4″ thick; 1 small onion, chopped, and 1/4 cup red or green bell pepper, chopped until tender. You can do this in a pan or in the microwave. I prefer to sauté the vegetables together so they develop a nice flavor.

If you do cook the vegetables in the microwave, be sure you add a little water to the bottom of a microwave-safe dish so the vegetables don’t dry out.

To make the egg mixture, BEAT together 2 eggs, 1 cup mayonnaise, ¼ teaspoon thyme and salt and pepper to taste.

COMBINE the egg mixture with the cooked vegetables and POUR into a greased 2 qt. casserole dish.

TOP the zucchini and yellow squash casserole with ¾ cup grated parmesan cheese and dot with 2 tablespoons butter.

BAKE at 375º for 25 minutes, until puffy and brown.

Zuchini squash bake in a casserole dish.


How do you keep squash casserole from getting watery?

Pre-cooking the squash in a skillet or microwave allows you to drain off any excess moisture before assembling the casserole.

You can also use salt to extract excess moisture before cooking.

Do this by cutting the zucchini into strips or rounds and sprinkling with a little salt. Lay the zucchini out on a paper towel and let sit for about half an hour, then rinse and pat dry.

Is zucchini healthier than yellow squash?

Zucchini and yellow squash are very similar. They have virtually the same nutritional value, flavor and texture.

The main differences are color, shape and the amount of seeds.

Zucchini are dark green, light green or golden. They are typically strait and don’t have a lot of seeds.

Yellow squash is yellow and typically has slight bell shape. They also have a lot more seeds.

What meat goes with squash casserole?

Squash casserole goes great with any meat like grilled chicken, meatloaf, brisket, ham and steak. Whatever you’ve got in the fridge will pair just fine!

Try this dish with my grilled balsamic bruschetta chicken and these cheesy drop biscuits.

Can I substitute zucchini for yellow squash?

If you only have one type of squash on hand you certainly don’t need to use both, I just like the contrasting colors the yellow and green provide!

Recipe Tips and Substitutions

Baked zucchini and squash on a wooden spoon.

I’m not a big fan of onions (or peppers for that matter). When I make this recipe again I’ll be using onion powder instead of the vegetable.

If you do like the flavor the onion and pepper provides, you can sautee them with the squash until tender and then discard them afterward.

Instead of full-fat mayo you can use a low fat or olive oil version, but it may not mix well or taste the same. The hard and fast rule with low-fat replacements is that they’ll never be quite as creamy as the original.

You can always use margarine instead of butter, but the note above about low-fat foods also applies.

Shredded parmesan cheese would also make a delicious crust if you don’t have grated on hand.

This recipe can be made ahead and chilled in the fridge. If you do make it ahead, it will need to cook for 30 minutes.

What can I do with so many zucchini?

Want more zucchini recipes? Try these!

I hope your family loves this zucchini and yellow squash casserole! If you make it, be sure to take a picture and tag me on Instagram with @ashcroftfamilytable and use the hashtag #ashcroftfamilytable.


And if you’d like to get a 4-week meal plan featuring my recipes, just enter your email in the form above and you’ll get it straight to your inbox!

Baked zucchini and squash on a wooden spoon.

Posh Squash (Zucchini and Yellow Squash Casserole)

The Ashcroft Family Table
4.67 from 3 votes
Prep Time 15 mins
Cook Time 25 mins
Total Time 40 mins
Course Side Dish
Cuisine American
Servings 6 -8 servings
Calories 300 kcal


  • 1 pound each zucchini and summer squash, sliced 1/4″ thick
  • 1 small onion, chopped
  • 1/4 cup red or green bell pepper, chopped
  • 2 eggs
  • 1 cup mayonnaise
  • 1/4 teaspoon thyme
  • 3/4 cup grated parmesan cheese
  • 2 tablespoons butter
  • Salt and pepper


  • Cook squash, onion, and bell pepper on the stove or in the microwave until tender.
  • In a medium-sized bowl, beat eggs, then blend in mayonnaise, thyme, salt and pepper.
  • Stir in squash.
  • Pour the mixture into a 2 qt. casserole dish.
  • Sprinkle evenly with parmesan cheese and dot with butter.
  • Bake uncovered at 375º for 25 minutes until puffy and brown.


  • If cooking vegetables in the microwave, be sure to use a microwave-safe dish with a cover. Add some water to the bottom of the dish so the vegetables don’t dry out.
  • This dish can be made ahead and chilled in the fridge.
  • If refrigerated, bake for 30 minutes instead of 25.


Serving: 1gCalories: 300kcalCarbohydrates: 8gProtein: 6gFat: 28gSaturated Fat: 7gPolyunsaturated Fat: 20gCholesterol: 74mgSodium: 425mgFiber: 2gSugar: 4g
Keyword posh squash, summer squash, zucchini, zucchini and yellow squash casserole
Tried this recipe?Let us know how it was!
Pinterest graphic with text, a spoonful of squash casserole, and zucchini and yellow squash in a dish.
Recipe Rating

scroll top arrow