Baked Zucchini Spinach Feta Casserole

The smell of onions and garlic hitting warm olive oil still makes my kitchen feel complete. I stumbled onto this casserole during a summer when my garden produced more zucchini than I knew what to do with, and now I actually find myself hoping for an overabundant harvest.

Last summer my neighbor called me over with an armful of zucchini from her garden. We made this together on her back porch while her kids ran through the sprinkler, and Ive been making it for my own family ever since.

Ingredients

• 2 medium zucchinis, sliced into rounds: Thin, even slices cook through evenly and layer beautifully
• 5 oz fresh baby spinach: Wilts down dramatically so buy more than you think you need
• 1 small onion, finely chopped: The foundation of flavor that sweetens as it sautés
• 2 garlic cloves, minced: Add after the onion so it doesnt burn and turn bitter
• 6 oz feta cheese, crumbled: Briny and tangy, it cuts through the richness of the other cheeses
• 1 cup grated mozzarella cheese: Creates those irresistible cheese pulls when you serve it
• 4 large eggs: Room temperature eggs incorporate more smoothly into the custard
• 3/4 cup whole milk: The fat helps the custard set up creamy and tender
• 2 tbsp extra virgin olive oil: Use half for cooking and drizzle the rest on top before baking
• 1/2 tsp dried oregano: Aromatic and classic Mediterranean flavor
• 1/4 tsp ground black pepper and salt: Adjust to your taste since feta is already salty
• 1/4 tsp crushed red pepper flakes: Optional but adds a gentle warmth that lingers
• 1 tbsp butter for greasing: Butter gives the crust better flavor and release than oil alone

Instructions

Preheat and prep your dish:

Heat your oven to 375°F and coat a 9x9-inch baking dish with butter, getting into all the corners.

Soften the aromatics:

Warm olive oil in a large skillet over medium heat, cook the onion for 3 minutes until translucent, then add garlic for just 1 minute until fragrant.

Wilt the spinach:

Toss in the spinach and stir constantly for about 2 minutes until it collapses into a dark green mass, then set it aside to cool slightly.

Whisk the custard:

Beat the eggs, milk, oregano, pepper, and salt together until the mixture is uniform and slightly frothy.

Build the first layer:

Arrange half the zucchini slices across the bottom of your dish, then spread half the spinach mixture on top and sprinkle with half of both cheeses.

Repeat the layers:

Add another layer of zucchini, the remaining spinach, and the rest of the cheese, pressing down gently as you go.

Add the custard and finish:

Pour the egg mixture slowly and evenly over everything, drizzle with the remaining olive oil, and add red pepper flakes if you like heat.

Bake until golden:

Bake uncovered for 35 minutes until the top is burnished brown and the center is set with no jiggle.

Rest before serving:

Let the casserole sit for 10 minutes so the custard firms up and slices hold their shape.

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This has become my go-to when friends drop by unexpectedly because it looks impressive but barely requires attention once its in the oven.

Make It Your Own

Sometimes I add fresh dill or basil right before baking, and during tomato season I scatter sliced cherry tomatoes between the layers. The custard keeps everything tender while the vegetables release their own sweetness into the dish.

Cheese Variations

My sister insists on adding Parmesan to the top layer for extra saltiness, while my husband prefers substituting Gruyère for the mozzarella when he wants something more assertive. Whatever you choose, buy blocks and grate them yourself for the best melt.

Serving Suggestions

This casserole is substantial enough to stand alone as a light dinner with a simple green salad dressed in lemon and olive oil. I also like serving it alongside roasted potatoes or crusty bread to soak up the creamy custard at the bottom of the dish.

• Leftovers reheat beautifully and actually taste better the next day
• Cut it into smaller squares as part of a Mediterranean mezze spread
• Pair with a crisp white wine like Assyrtiko or Pinot Grigio

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Theres something deeply satisfying about turning a few humble vegetables into a dish that feels like a celebration of summer.

Recipe FAQs

→ Can I prepare this casserole ahead of time?

Yes, you can assemble the entire casserole up to 24 hours in advance and refrigerate it before baking. Add about 5-10 minutes to the baking time if baking straight from the refrigerator.

→ Can I freeze leftovers?

Absolutely. Portion leftovers into airtight containers and freeze for up to 3 months. Thaw overnight in the refrigerator and reheat in a 350°F oven until warmed through.

→ What can I substitute for feta cheese?

Goat cheese or ricotta work well as alternatives. For a dairy-free version, try vegan feta or crumbled firm tofu seasoned with lemon juice and herbs.

→ How do I know when the casserole is done?

The casserole is ready when the top is golden brown, the edges are bubbling, and a knife inserted into the center comes out clean. The eggs should be fully set.

→ Can I add other vegetables?

Certainly. Bell peppers, mushrooms, or artichoke hearts make excellent additions. Just ensure vegetables are cooked or sautéed before layering to avoid excess moisture.

→ Is this dish keto-friendly?

With only 9g carbohydrates per serving, this casserole fits well into a ketogenic diet. The combination of eggs, cheese, and low-carb vegetables makes it ideal for low-carb eating.