Posh Squash (The Yummiest Zucchini and Yellow Squash Casserole)

July 16, 2020

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.


For this easy zucchini and squash recipe you’ll need zucchini and squash (of course!), onion, green or red bell pepper, eggs, mayo, thyme, parmesan cheese, and butter.

How to Make Posh Squash

First, you’ll need to cook the squash, onion, and pepper until tender. You can do this in a pan or in the microwave. I prefer to sautee 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, you’ll beat the eggs and add the mayo, thyme, and some salt and pepper. That gets combined with the cooked vegetables and poured in a greased 2 qt. casserole dish.

To finish the zucchini and yellow squash casserole, sprinkle with parmesan and dot with butter. It bakes for 25 minutes until puffy and brown.

Zuchini squash bake in a casserole dish.

Recipe Tips and Substitutions

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.

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.

Baked zucchini and squash on a wooden spoon.

What can I do with so many zucchini?

If you’re looking for another side dish for zucchini, try sauteeing it with some onions and eggs.

This zucchini and yellow sqaush casserole dish pairs well with:

I hope your family loves this recipe! 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)

Yield: 6-8 servings
Prep Time: 15 minutes
Cook Time: 25 minutes
Total Time: 40 minutes


  • 2 lbs 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


  1. Cook squash, onion, and bell pepper on the stove or in the microwave until tender.
  2. In a medium-sized bowl, beat eggs, then blend in mayonnaise, thyme, salt and pepper.
  3. Stir in squash.
  4. Pour the mixture into a 2 qt. casserole dish.
  5. Sprinkle evenly with parmesan cheese and dot with butter.
  6. 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.

Nutrition Information:
Yield: 8 Serving Size: 1
Amount Per Serving: Calories: 300Total Fat: 28gSaturated Fat: 7gTrans Fat: 0gUnsaturated Fat: 20gCholesterol: 74mgSodium: 425mgCarbohydrates: 8gFiber: 2gSugar: 4gProtein: 6g
If you're looking for zucchini and yellow squash recipes, Posh Squash is a great baked side dish.

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