Preheat oven to 375°F (190°C). Cook ziti according to package directions.
In a large bowl, combine ricotta cheese, mozzarella cheese, oregano, and garlic powder.
In a 9x13 inch baking dish, spread half of the marinara sauce.
Layer half of the cooked ziti over the sauce, followed by half of the ricotta mixture.
Repeat layers with remaining ziti, ricotta mixture, and marinara sauce.
Bake for 30-40 minutes, or until heated through and bubbly.