Baked Zucchini Spinach Feta Casserole

The smell of onions and garlic hitting olive oil still stops me in my tracks every time. I first threw this casserole together on a Tuesday when my CSA box delivered more zucchini than I knew what to do with. Now it is the kind of dinner that makes people ask when I am making it again.

My sister took one bite and asked for the recipe before she even finished chewing. I have made this for potlucks, weeknight dinners, and even a holiday brunch. Every single time the dish comes back empty.

Ingredients

• 2 medium zucchinis, sliced into rounds: Thin slices cook through evenly and layer beautifully
• 5 oz fresh baby spinach: Wilts down to just the right amount without overwhelming the dish
• 1 small onion, finely chopped: Creates a sweet aromatic base for the vegetables
• 2 garlic cloves, minced: Blooms in the hot oil for mellow garlic flavor throughout
• 6 oz feta cheese, crumbled: Brings tang and salt that ties everything together
• 1 cup grated mozzarella cheese: Melts into gooey strands and holds layers together
• 4 large eggs: The binder that turns vegetables into a cohesive casserole
• 3/4 cup whole or 2 percent milk: Creates a custardy texture as it bakes
• 2 tbsp extra virgin olive oil: One for cooking vegetables, one for drizzling on top
• 1/2 tsp dried oregano, 1/4 tsp black pepper, and 1/4 tsp salt: Simple Mediterranean seasoning that complements rather than competes
• 1/4 tsp crushed red pepper flakes: Optional but adds a lovely warmth
• 1 tbsp butter or olive oil for greasing: Ensures nothing sticks to the baking dish

Instructions

Preheat your oven and prepare the dish:

Get your oven to 375 degrees and butter a 9 by 9 inch baking dish thoroughly.

Cook the aromatics:

Warm 1 tablespoon olive oil in a large skillet over medium heat, cook the onion 3 minutes until soft, add garlic for 1 minute more.

Wilt the spinach:

Toss in the spinach and stir until it collapses, about 2 minutes, then set aside to cool slightly.

Whisk the custard:

Beat eggs with milk, oregano, pepper, and salt until well combined.

Build the first layer:

Arrange half the zucchini slices in the dish, top with half the spinach mixture, then half the feta and mozzarella.

Repeat the layers:

Add remaining zucchini, spinach, feta, and mozzarella in the same order.

Pour and finish:

Evenly pour the egg mixture over everything, drizzle with remaining olive oil, and sprinkle red pepper flakes if using.

Bake until golden:

Bake uncovered 35 minutes until set and golden brown on top.

Rest before serving:

Let the casserole sit 10 minutes so it firms up for clean slices.

Save

This recipe saved me during a month when I was too tired to think about dinner but still wanted something satisfying. Now it is my go to for feeding a crowd without spending all day in the kitchen.

Making It Your Own

Fresh herbs like dill, parsley, or basil brighten the flavors and add a pop of color against the golden cheese. I have swapped mozzarella for Gruyère when I wanted something sharper, and Monterey Jack works beautifully for a milder finish. The vegetables are flexible too. Yellow squash, sliced mushrooms, or even roasted red peppers can join the zucchini without changing the bake time.

What to Serve Alongside

A crisp green salad with an acidic vinaigrette cuts through the rich cheese and eggs. Crusty bread is perfect for sopping up any custard left on the plate. For a complete Mediterranean spread, add roasted potatoes or simple roasted tomatoes on the side.

Make Ahead Wisdom

You can assemble the entire casserole up to a day before baking and keep it covered in the refrigerator. The texture actually benefits from sitting as the flavors meld together. If baking cold, add about 10 minutes to the cooking time.

• Leftovers reheat beautifully in a 350 degree oven for 15 minutes
• The casserole freezes well for up to 2 months if wrapped tightly
• Wrap individual portions for quick work lunches throughout the week

Save

There is something deeply satisfying about a vegetarian dish that feels substantial and complete. This casserole has become a regular in my rotation, and I hope it finds a permanent place in yours too.

Recipe Questions

→ Can I prepare this casserole ahead of time?

Yes, assemble the entire casserole up to 24 hours in advance and refrigerate unbaked. Add 5-10 minutes to the baking time if baking cold from the refrigerator.

→ How do I store leftovers?

Store cooled leftovers in an airtight container in the refrigerator for 3-4 days. Reheat individual portions in the microwave or cover the entire dish with foil and warm in a 350°F oven.

→ Can I freeze this casserole?

Freeze unbaked for up to 3 months. Thaw overnight in the refrigerator before baking. Baked portions can also be frozen for 2 months, though the texture may become slightly softer.

→ What can I use instead of feta cheese?

Goat cheese, ricotta salata, or halloumi work well as alternatives. For a dairy-free version, try firm tofu crumbled with lemon juice and herbs, though the flavor profile will change.

→ How do I know when the casserole is done?

The casserole is finished when the center is set and no longer jiggles, the top is golden brown, and a knife inserted in the center comes out clean. The internal temperature should reach 160°F.

→ Can I add other vegetables?

Absolutely. Bell peppers, mushrooms, artichoke hearts, or diced eggplant make excellent additions. Sauté harder vegetables like peppers before layering to ensure they cook through.