Preheat your oven to 375°F (190°C) while greasing a 9x13-inch baking dish with a thin layer of butter.

In a large mixing bowl, combine the sliced medium zucchinis, chopped fresh spinach, and minced garlic. Drizzle with olive oil and toss gently.

In another bowl, whisk together the ricotta cheese, large eggs, crumbled feta, dried oregano, basil, salt, and pepper until smooth.

Spread half of the zucchini and spinach mixture evenly across the bottom of the prepared baking dish, pressing down gently.

Spoon half of the cheese mixture over the first layer of vegetables, spreading it out evenly.

Layer the remaining zucchini mixture on top of the first cheese layer, pressing down lightly.

Spread the remaining cheese mixture atop the zucchini layer.

In a small bowl, combine the breadcrumbs with grated Parmesan cheese. Sprinkle this mixture over the top of the casserole.

Place the baking dish in your preheated oven and bake for 35-40 minutes, until the top is golden brown.

Once baked, let the casserole cool for a few minutes before slicing and serving warm.