Preheat oven to 350°F. Cook pasta according to package directions.
In a medium sized bowl, mix ricotta cheese, Parmesan cheese, egg, salt, and pepper together until thoroughly blended. Stuff shells or manicotti with cheese mixture.
Place stuffed shells in a 13" x 9" baking dish lightly coated with non-stick cooking spray. Spoon marinara sauce over each shell; sprinkle with mozzarella cheese. Bake for 20-30 minutes or until bubbly.