Preheat oven to 350 degrees.
Boil water and cook shells according to directions on package. Drain the shells, spray them with cooking spray (to prevent sticking) and set aside.
In a medium bowl, mix ricotta, egg, Italian seasoning and 1 cup of mozzarella until combined well.
Fill each shell with a tablespoon of the ricotta mixture.
Spray a 9×13 casserole dish. Fill the casserole dish with the stuffed shells. You can fit four rows of five shells.
Pour 1 cup of marinara sauce over the stuffed shells.
Sprinkle remaining 1 cup of shredded mozzarella over the sauce.
Cover with foil and bake for 30 minutes in a 350 degree oven.
Remove foil and bake for another 5 minutes.