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

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

Add the ground beef or sausage to the skillet, breaking it apart and cooking until browned. Stir in the marinara sauce and Italian seasoning, then let it simmer to blend the flavors.

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

Grease a baking dish. Layer half of the cooked ziti, spread half of the ricotta mixture evenly, sprinkle with half of the mozzarella cheese, and add half of the sauce.

Repeat these layers, finishing with a generous topping of the remaining mozzarella and Parmesan cheese.

Cover the baking dish with foil and bake in a preheated oven at 375°F (190°C) for 20 minutes.

Remove the foil and continue baking for another 10-15 minutes until the cheese is bubbly and browned.

Let rest for 5 minutes before serving.