Preheat oven to 350°F (175°C).
Cook manicotti shells according to package instructions. Drain and set aside.
In a mixing bowl, combine ricotta, 1 cup mozzarella, ½ cup Parmesan, garlic, salt, and pepper.
Stuff manicotti shells with the cheese mixture.
Spread a thin layer of marinara sauce on the bottom of a baking dish.
Place stuffed shells in the baking dish and cover with remaining marinara sauce.
Sprinkle remaining mozzarella and Parmesan on top.
Cover with foil and bake for 30 minutes. Remove foil and bake for an additional 10 minutes, until cheese is bubbly and golden.
Let cool for a few minutes before serving.