Preheat the oven to 375°F. Bring a large pot of salted water to a boil and cook the ziti until al dente. Drain and set aside.
Heat the olive oil in a skillet over medium heat. Add the minced garlic and cook for about 1 minute. Stir in the marinara sauce and let it warm through for 3 minutes.
In a mixing bowl, combine the ricotta cheese with the oregano, salt, and black pepper.
Spread a thin layer of sauce in the bottom of a baking dish. Add half the cooked pasta, then spoon half the ricotta mixture over the top in small dollops. Add more sauce and half the mozzarella. Repeat the layers once more and finish with the remaining mozzarella and Parmesan.
Bake uncovered for 25 minutes, or until the cheese is melted and starting to brown on top.