This cheesy baked Zucchini Casserole is absolutely delicious and simple to make.
I’m always experimenting with zucchini and find new ways to enjoy this versatile squash. Whether sliced, spiralized, or baked, zucchini adapts well to many flavors and cooking methods.
Some favorite preparations include turning zucchini into warm chicken zoodle soup or baking it with lemon, basil and feta for a bright side dish. This casserole combines tender slices of zucchini with a rich, caramelized onion cream sauce and a golden, cheesy topping for a comforting cold-weather meal.
The recipe below makes about eight side-dish servings. If you prefer fewer leftovers, you can halve the ingredients to serve a smaller group.
Baked Zucchini Casserole
A simple, cheesy vegetarian side dish that pairs well with weeknight dinners or holiday spreads.
Zucchini Casserole
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Ingredients
- 1 lb zucchini squash
- 2 cups finely diced onion
- 1 tsp olive oil
- 3 TBSP butter
- 3 TBSP all-purpose flour
- ¾ cup milk (warmed)
- ¼ tsp salt (plus more to taste)
- ¼ tsp black pepper (plus extra to taste)
- ¼ tsp garlic powder
- ⅛ tsp ground nutmeg
- 4 oz freshly grated Gruyere cheese
- 4 oz freshly grated Gouda cheese
Crispy Italian Breadcrumb Topping
- ½ cup Italian seasoned breadcrumbs (panko or regular)
- 1 TBSP unsalted butter
Instructions
Prep Work
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Measure all ingredients before you begin; the sauce comes together quickly.
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Trim the zucchini ends and slice into 1/4-inch rounds. Avoid slicing too thin to prevent mushy texture. For smaller bites, halve the rounds lengthwise.
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Sprinkle the zucchini slices with sea salt and place them on a clean, absorbent dish towel. Let sit at least 15 minutes (30–40 minutes draws out more water). Pat dry with paper towels to remove excess moisture.
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Preheat the oven to 375°F.
Get Cooking
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Heat a medium pot over medium-high heat with 1 tsp olive oil. Sauté the diced onions, stirring occasionally, until golden brown and tender.
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Push the onions to the side, add 3 TBSP butter, and once melted whisk in the flour. Cook, whisking constantly, for about 2 minutes until the roux darkens slightly. Gradually whisk in warmed milk and bring to a light boil, whisking for about 1 minute until the sauce thickens.
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Remove the pot from heat and add salt, pepper, garlic powder, and nutmeg. In two to three batches, whisk in half the Gruyere and all the Gouda until melted and smooth.
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Arrange the zucchini in a medium baking dish, pour the cheese-onion sauce over the top, and sprinkle with the remaining Gruyere. Bake at 375°F for 20–25 minutes, until the top is golden and the zucchini is tender.
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While the casserole bakes, toast the Italian-seasoned breadcrumbs in a small skillet with 1 TBSP butter until golden. Sprinkle the toasted crumbs over the casserole and return to the oven for a few minutes to finish.
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Serve hot and enjoy.
Notes
Nutrition facts are estimates calculated with an online tool; adjust as needed.
Nutrition
If you try this cheesy baked zucchini casserole, I’d love to hear how it turned out. Leave a comment or tag your photos so the author can see your version.
Have extra zucchini to use?
Try other vegetarian zucchini recipes such as Zucchini Parmesan, Hasselback Zucchini Pizzas for a kid-friendly option, or zucchini-studded Veggie Burgers for make-ahead meals. These variations are great for using up an abundance of zucchini and provide different textures and flavors to enjoy.