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!
$8.88 per recipe / $1.11 per serving

My husband’s grandma sure knows how to cook!
She has some of the most amazing recipes and Posh Squash is one of them.
This zucchini and yellow squash casserole works because it’s:
- Delicious and tasty. Sauteeing the vegetables gives them extra flavor and the seasonings take it to another level.
- A great way to use garden vegetables. If you ever have zucchini that you don’t know what to do with, just make this casserole.
- The perfect side dish. This recipe pairs well with most meats and is a great way to get your family to eat their vegetables.
Step-by-Step Instructions

Preheat oven to 375 degrees.
Cook 1 pound each of zucchini and summer squash, sliced 1/4″ thick, 1 small onion, chopped, and 1/4 cup 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 1 teaspoon salt, and ½ teaspoon pepper.

Combine the egg mixture with the cooked vegetables and pour into a greased 2 quart casserole dish.

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

Bake at 375 degrees for 25 minutes, until puffy and brown.
Recipe Tips and Substitutions

If you’re not a big fan of onions you can make this recipe again using onion powder instead of the vegetable.
If you do like the flavor the onion and pepper provide, 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.
Try these substitutes if you’re out of any ingredients:
More Like This

Want more zucchini recipes? Try these!
- Chicken Zucchini Casserole with Stuffing
- Scrambled Eggs with Zucchini
- Grilled Sausage Kabobs with a Honey Mustard Glaze
- Zucchini, Black Bean, and Rice Skillet
- Italian Ground Turkey Patties with Vegetables
Recipe Costs
This recipe costs $8.88 to make which is $1.11 a serving! If you grow your own produce, this recipe will be even cheaper!
- Zucchini – $1.69
- Summer squash – $1.69
- Onion – $0.60
- Bell pepper – $0.40
- Eggs – $0.50
- Mayonnaise – $2.38 (get the avocado mayo in bulk at Costco to save money!)
- Dried thyme $0.05
- Salt and pepper – $0.05
- Parmesan cheese -$1.20
- Butter – $0.32
FAQ’s

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.
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 number of seeds.
Zucchini are dark green, light green, or golden. They are typically straight and don’t have a lot of seeds.
Yellow squash is yellow and typically has a slight bell shape. They also have a lot more seeds.
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!
An example of a meal I would serve with this casserole is steak with a side of roasted sweet potatoes and apples and cheesy drop biscuits.
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 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!

Posh Squash (Zucchini and Yellow Squash Casserole)
Ingredients
- 1 pound zucchini , sliced 1/4" thick
- 1 pound summer squash, sliced 1/4" thick
- 1 small onion, chopped
- ¼ cup bell pepper (any color), chopped
- 2 eggs
- 1 cup mayonnaise
- ¼ teaspoon dried thyme
- 1 teaspoon salt
- ½ teaspoon pepper
- ¾ cup grated parmesan cheese
- 2 tablespoons butter
Instructions
- Preheat oven to 375 degrees.
- Cook squash, onion, and bell pepper in a frying pan on the stove or in the microwave until tender.
- In a medium-sized bowl, beat eggs, then blend in mayonnaise, thyme, salt and pepper.
- Add squash and vegetables to the egg mixture and stir until well combined.
- Pour the mixture into a 2-quart casserole dish.
- Sprinkle the squash evenly with parmesan cheese and dot with butter.
- Bake uncovered at 375 degrees for 25 minutes until puffy and brown.
Video
Notes
- 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.