Bring a large pot of salted water to a boil. Add the ziti and cook until al dente, about 8 minutes. Drain and set aside.

In a large skillet, heat the olive oil over medium heat. Add the chopped onions and minced garlic. Sauté until fragrant and translucent.

If using ground beef or sausage, add it now, breaking it up and cooking until browned. Stir in the marinara sauce and Italian seasoning, letting it simmer for a few minutes.

In a separate bowl, combine the ricotta cheese, large egg, half the grated Parmesan, salt, and pepper. Mix until smooth and creamy.

Grease the baking dish. Start with half of the ziti, then spread half of the ricotta mixture over it. Sprinkle with half of the mozzarella, then half of the sauce. Repeat the layering, finishing with the remaining mozzarella and Parmesan.

Cover the dish with foil and bake in a preheated oven at 375°F (190°C) for 20 minutes. Remove the foil and bake for another 10-15 minutes until the cheese is bubbly and lightly browned.

Let it rest for about 5 minutes before serving.