Preheat your oven to 350°F (175°C).
Cook the manicotti shells according to the package instructions. Drain and set aside.
In a mixing bowl, combine ricotta cheese, ½ cup mozzarella cheese, Parmesan cheese, beaten egg, salt, pepper, and parsley.
Stuff each manicotti shell with the cheese mixture.
Spread 1 cup of marinara sauce on the bottom of a baking dish.
Place the stuffed shells in the baking dish and cover with the remaining marinara sauce.
Sprinkle the remaining mozzarella cheese on top.
Bake in the preheated oven for 30-40 minutes, or until the cheese is melted and bubbly.
Let it cool for a few minutes before serving. Enjoy!