Brown meat in a medium skillet until cooked. Drain off the fat. I dump it in a collander and let it drain and get cool. Put it back in your skillet (why dirty a bowl)? Add egg and Mozzarella cheese and mix well by hand.
Pour 2 cups of sauce into a 13x9x2 pan. Fill the shells with meat mixture and place on top of sauce side by side. Spread leftover filling in open areas. Pour remaining sauce over shells and pour 1 cup of water over everything.
Cover with foil and bake for 50 minutes at 375*. Allow to stand an additional 10 minutes before serving.