Preheat oven to 375°F (190°C).
Cook pasta shells according to package directions. Drain and set aside.
In a mixing bowl, combine ricotta, mozzarella, Parmesan, egg, garlic powder, basil, oregano, salt, and pepper.
Fill each shell with the cheese mixture.
Spread 1 cup of marinara sauce on the bottom of a baking dish.
Arrange stuffed shells in the dish and top with remaining marinara sauce.
Cover with foil and bake for 25 minutes. Remove foil and bake for an additional 5 minutes.
Let cool for a few minutes before serving.