Preheat the oven to 375°F (190°C).
Cook the ziti pasta according to package instructions until al dente.
In a large skillet, heat olive oil over medium heat and sauté the minced garlic for 1 minute.
Add the Italian sausage to the skillet, breaking it into smaller pieces, and cook until browned and cooked through.
Stir in the marinara sauce and oregano, letting it simmer for 5 minutes.
In a large bowl, combine cooked ziti, ricotta cheese, and a portion of the mozzarella, mixing gently.
Add the sausage and marinara mixture to the pasta mixture, stirring until well combined.
Transfer the mixture to a greased baking dish and spread it out evenly.
Top with remaining mozzarella and sprinkle with Parmesan cheese.
Cover with aluminum foil and bake for 25 minutes, then uncover and bake for an additional 15 minutes.
Let the baked ziti rest for 10 minutes before serving.