Preheat the oven to 375°F (190°C).

In a mixing bowl, combine ricotta cheese, half of the mozzarella, oregano, salt, and pepper.

In a skillet, heat olive oil over medium heat and sauté onions and garlic until translucent.

Add sliced zucchini to the skillet and cook for about 5 minutes until slightly softened.

In a baking dish, layer half of the zucchini mixture, then spread the ricotta mixture on top.

Add the remaining zucchini mixture and top with bread crumbs and the rest of the mozzarella and Parmesan cheese.

Bake in the preheated oven for 25-30 minutes until golden and bubbly.