Baked Zucchini Spinach Feta Casserole

The first time I made this casserole, I was trying to use up a massive zucchini harvest from my garden. My kitchen counters were covered in these green summer squash, and I needed something that could transform them into dinner fast. This recipe ended up being so good that my husband asked when we were having it again before he'd even finished his first serving.

Last summer I made this for a potluck when three friends announced they were vegetarian. I was worried it would feel too simple alongside everyone else's elaborate dishes, but the platter came back empty. Two people actually messaged me the next day asking for the recipe.

Ingredients

• 2 medium zucchinis, sliced into 1/4 inch rounds: Thinner slices cook through evenly and layer beautifully without turning mushy
• 5 oz fresh baby spinach: The baby leaves are tender and wilt quickly, plus they need no stemming or chopping
• 1 small onion, finely chopped: Red onion works beautifully here and adds lovely color throughout the layers
• 2 garlic cloves, minced: Fresh garlic matters since it infuses the whole casserole as it bakes
• 6 oz feta cheese, crumbled: Buy a block and crumble it yourself for better texture and bigger salty pockets
• 1 cup grated mozzarella cheese: This creates that gorgeous golden melted top everyone reaches for first
• 4 large eggs: Room temperature eggs whisk into a smoother, more cohesive custard
• 3/4 cup whole milk: The richness here really does make a difference in the final texture
• 2 tbsp extra virgin olive oil: Use the good stuff since the flavor carries through the entire dish
• 1/2 tsp dried oregano: Fresh oregano works wonderfully too, just use about 1 tbsp chopped
• 1/4 tsp ground black pepper: Freshly cracked pepper adds little bursts of spice throughout
• 1/4 tsp salt: The feta is already salty, so taste before adding more
• 1/4 tsp crushed red pepper flakes: This tiny kick makes everything else sing without overwhelming

Instructions

Get your oven ready:

Preheat to 375°F and generously butter a 9x9 inch baking dish, getting into all the corners

Sauté the aromatics:

Heat 1 tbsp olive oil in a large skillet over medium heat, cook onion for 3 minutes until translucent, then add garlic for 1 minute until fragrant

Wilt the spinach:

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

Whisk the custard:

In a large bowl, beat eggs with milk, oregano, pepper, and salt until thoroughly combined

Build the first layer:

Arrange half the zucchini slices in the dish, spread half the spinach mixture over them, then scatter with 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 on top

Bake to golden:

Bake uncovered for 35 minutes until the center is set and the top is bubbling with golden patches

The waiting game:

Let it rest for 10 minutes before slicing, which helps the custard set and makes serving much easier

Save

This became my go-to when my sister had her third baby and I was bringing dinner to their house. She texted me weeks later saying it was the first meal her toddler actually asked for seconds of, which felt like the biggest win.

Make It Ahead

I've assembled this casserole the night before and stored it covered in the refrigerator. The flavors actually meld together better, and it's such a relief to just pop it in the oven when guests arrive.

Serving Suggestions

A simple green salad with lemon vinaigrette cuts through the richness beautifully. I also love serving this with warm crusty bread to soak up any custardy bits left on the plate.

Freezing Instructions

Leftovers freeze surprisingly well, just wrap individual portions tightly. I've learned to re-wrap in foil when reheating to prevent the cheese from drying out.

• Double the recipe and freeze half for those nights you just cannot cook
• Thaw overnight in the refrigerator before reheating at 350°F for 20 minutes
• Add 5 minutes to the baking time if baking from frozen

Save

There's something deeply comforting about a dish that comes out of the oven looking this beautiful and tasting even better. Hope it becomes a staple in your kitchen like it has in mine.

Questions & Answers

→ Can I make this casserole ahead of time?

Yes, you can assemble the casserole up to 24 hours in advance and refrigerate it before baking. Add an extra 5-10 minutes to the baking time if baking from cold.

→ What can I substitute for feta cheese?

Goat cheese or ricotta can replace feta for a milder flavor. For a dairy-free option, try vegan feta or crumbled firm tofu seasoned with herbs and lemon.

→ How do I prevent the casserole from being watery?

Sauté the spinach until completely wilted and drain any excess liquid before layering. Also, try to slice zucchini evenly and pat them dry with paper towels if they seem especially moist.

→ Can I freeze leftovers?

Leftovers freeze well for up to 3 months. Cut into portions, wrap tightly in plastic and foil, then thaw overnight in the refrigerator before reheating at 350°F until warmed through.

→ What herbs work best in this dish?

Fresh dill, parsley, or basil complement the Mediterranean flavors beautifully. Add them during assembly or sprinkle on top during the last 5 minutes of baking.

→ Is this suitable for low-carb diets?

Yes, this casserole is naturally low in carbohydrates with only 9g per serving. It's perfect for keto or low-carb meal plans when enjoyed as a main course.