Preheat your oven to 375°F.

Bring a large pot of salted water to a boiling point. Add the pasta and cook according to package directions, about 8 to 10 minutes until just al dente. Drain well and set aside.

In a large skillet, heat olive oil over medium heat. Sauté the diced onion and minced garlic for 3 to 4 minutes until soft and translucent.

Add the chopped spinach to the skillet and stir it occasionally as it wilts, which usually takes about 2 to 3 minutes.

In a large mixing bowl, combine the ricotta cheese, half of the mozzarella, half of the Parmesan, egg, dried oregano, salt, and black pepper. Mix until smooth and creamy.

Fold the cooked pasta and spinach mixture into the ricotta mix. Stir gently until well incorporated.

Grease a 9x13-inch baking dish with olive oil. Pour the pasta-ricotta mixture into the dish and spread evenly. Top with remaining mozzarella and Parmesan.

Bake for 25 to 30 minutes until the top is bubbly and golden.

Let it rest for 5 minutes before serving.