Preheat your oven to 375°F (190°C).
Cook the manicotti pasta according to package instructions until al dente.
In a bowl, mix ricotta, mozzarella, Parmesan, egg, Italian seasoning, salt, and pepper.
Fill each manicotti tube with the cheese mixture using a piping bag or spoon.
Spread a thin layer of marinara sauce on the bottom of a baking dish.
Arrange stuffed manicotti in the dish, side by side.
Cover the manicotti with the remaining marinara sauce.
Sprinkle additional mozzarella cheese on top.
Cover with foil and bake for 20 minutes.
Remove foil and bake for an additional 10 minutes until bubbly and golden.