Preheat oven to 180 degrees
Pour 2½ cups of the marinara sauce in the bottom of a large baking dish and set aside.
In a large bowl, mix together the cooked beef, egg, breadcrumbs, pepperoni, 1/2 cup of mozzarella, parsley, oregano, Parmesan cheese and remaining marinara sauce.
Stuff your prepped peppers with the filling, cover with foil and bake for 30 minutes. Remove the foil, top with the remaining mozzarella and bake for 15 more minutes, or until the cheese is golden brown and bubbly.
Let cool for a few minutes before serving and enjoy!