Preheat the oven to 375°F (190°C).
Cook the pasta shells according to package instructions until al dente. Drain and set aside.
In a mixing bowl, combine ricotta, mozzarella, Parmesan, egg, Italian seasoning, salt, and pepper.
Fill each pasta shell with the cheese mixture using a spoon or piping bag.
Spread 1 cup of marinara sauce on the bottom of a baking dish.
Arrange the stuffed shells in the dish, open side up.
Pour the remaining marinara sauce over the shells.
Cover with aluminum foil and bake for 20 minutes.
Remove the foil and bake for an additional 10 minutes until the cheese is bubbly.
Garnish with fresh parsley before serving.