Make zucchini casserole with fresh squash, savory seasoning, and a crisp baked topping for a simple dish that works well beside almost any supper.

This zucchini casserole turns an armful of fresh zucchini into a bubbling, golden dinner that smells like garlic, toasted Parmesan, and browned butter before it even reaches your plate!

Ingredients

For the zucchini filling

• 2½ pounds medium zucchini, approximately 5 to 6 zucchini, cut into ¼-inch-thick half-moons
• 1½ teaspoons kosher salt, divided
• 2 tablespoons extra-virgin olive oil, divided
• 1 medium yellow onion, finely diced
• 3 garlic cloves, finely minced
• ¾ teaspoon freshly ground black pepper
• 1 teaspoon Italian seasoning
• ¼ teaspoon red pepper flakes, optional
• 2 large eggs
• ¾ cup sour cream, preferably full-fat
• 1 tablespoon Dijon mustard
• 1 teaspoon finely grated lemon zest
• 1½ cups freshly shredded sharp cheddar cheese, divided
• ½ cup freshly grated Parmesan cheese, divided

For the crispy topping

• 1 cup coarsely crushed buttery crackers, approximately 24 round crackers
• 2 tablespoons unsalted butter, melted
• Remaining cheddar and Parmesan, reserved from amounts above
• 2 tablespoons chopped fresh parsley, for finishing

Servings: 6 generous servings

How to Make Zucchini Casserole

Heat oven to 375°F and lightly grease a 9 x 13-inch baking dish with 1 teaspoon olive oil or a thin coating of cooking spray. Place one oven rack in center position so casserole receives even heat without burning its topping before filling becomes hot.

Cut zucchini into ¼-inch half-moons, keeping pieces as even as reasonably possible. You do not need to stand over them with a ruler, but very thin slices will turn soft before thicker pieces finish cooking.

Place sliced zucchini in a large colander, sprinkle it with 1 teaspoon kosher salt, and toss well with your hands. Let it drain over a bowl or sink for 15 minutes.

Salt pulls moisture toward zucchini’s surface, which is exactly what we want before it enters casserole.

While zucchini drains, warm 1 tablespoon olive oil in a large skillet over medium heat. Add diced onion with remaining ½ teaspoon salt, then cook for 5 to 6 minutes, stirring occasionally.

Onion is ready when it looks translucent, smells sweet, and has a few pale golden edges. Lower heat slightly if garlic-sized dark spots begin appearing too quickly.

Add minced garlic, black pepper, Italian seasoning, and red pepper flakes. Stir for 30 to 45 seconds, just until garlic smells fragrant. Do not walk away here! Garlic can move from fragrant to bitter while you are checking one innocent notification.

Spread drained zucchini across a clean kitchen towel or several layers of paper towel, cover it, and press firmly to remove surface moisture.

You are not trying to crush zucchini or wring it out like laundry. A thorough press is enough. Don’t skip this step, because any water removed now is water that cannot dilute your creamy filling later.

Transfer cooked onion mixture to a large mixing bowl. Return skillet to medium-high heat and add remaining olive oil. Add zucchini in two batches so pieces have room to touch hot pan rather than steaming in a crowded pile.

Cook each batch for 3 to 4 minutes, turning occasionally, until zucchini is brighter green with a few lightly browned spots but still feels firm at its center. It should bend slightly when lifted, not collapse. Transfer each cooked batch to a plate and let it cool for about 5 minutes.

In a separate bowl, whisk eggs until no streaks of white remain. Add sour cream, Dijon mustard, and lemon zest, then whisk until mixture looks smooth and pale. Stir in 1 cup cheddar and ¼ cup Parmesan.

Adding hot zucchini directly to eggs could begin cooking them unevenly, so make sure vegetables have stopped steaming heavily before combining everything.

Add zucchini and onion mixture to creamy cheese mixture. Fold gently with a wide spatula until every piece has a light coating.

Scrape filling into prepared baking dish and spread it into an even layer, making sure zucchini reaches corners rather than forming a vegetable mountain in center.

Combine crushed crackers, melted butter, remaining ½ cup cheddar, and remaining ¼ cup Parmesan in a small bowl. Mix until crumbs feel lightly coated rather than soaked. Scatter topping evenly over casserole.

Keep layer loose and craggy instead of pressing it flat, since those uneven peaks become beautifully crisp in oven.

Bake uncovered for 25 to 30 minutes, until filling bubbles gently around edges and topping becomes golden brown. If your baking dish is deep or ingredients were still cold, casserole may need closer to 35 minutes.

Look for active bubbles in several places, not only one brave bubble near a corner. An instant-read thermometer inserted into center should register at least 160°F because filling contains eggs.

If filling is hot but topping needs more color, move dish to upper rack and broil for 30 to 90 seconds. Stay beside oven and watch continuously, because buttered crackers can turn from pale to charcoal with impressive ambition.

Remove casserole from oven and let it rest for 10 minutes before serving. This pause allows filling to settle and cheese sauce to thicken around zucchini.

Spoon it out immediately and it may appear loose, even when you prepared everything correctly. Finish with chopped parsley just before serving for fresh flavor and a pop of green.

Serving Suggestions

Serve this cheesy zucchini casserole with:

• Roasted chicken: Lemon and herb roasted chicken balances creamy casserole particularly well.
• Grilled pork chops: Smoky, browned pork works beautifully with mild zucchini and sharp cheddar.
• Baked salmon: Add a crisp green salad for a fresh, colorful dinner.
• Garlic bread: Useful for catching creamy sauce left on your plate, which is serious kitchen efficiency.
• Tomato salad: Juicy tomatoes, red onion, basil, and balsamic vinegar cut through rich cheese.
• Rice or quinoa: Either one turns casserole into a more substantial meatless meal.
• Fried or poached eggs: Leftover casserole with an egg makes an excellent savory breakfast or lunch.

For a complete vegetarian dinner, serve generous portions with a white bean salad or chickpeas dressed with lemon, olive oil, and fresh herbs.

This zucchini casserole is exactly what I want when fresh zucchini is piled high at markets or quietly multiplying in a garden: tender vegetables, sharp melted cheese, sweet onion, plenty of garlic, and a buttery crust that audibly crackles under a serving spoon!

Hungry for more feel-good meals? Explore these 21 Anti-Inflammatory Breakfast Recipes for a nourishing start and 10 Anti-Inflammatory Dinner Recipes for delicious evenings that make healthy eating easy!