Cut tops of peppers off and remove the insides. Using a spoon, thin the inside walls removing all membranes. Rinse. Put the peppers in boiling water and cover, for 5-7 mins. You want the peppers to be a little soft but not tearing apart. Remove from water and place opening side down on paper towels to cool.
In Large skillet, cook hamburger till brown. Drain. Add chopped onion (I like about 1/2 cup or a little more), Salt, Garlic (as much as you want according to your taste. I use at least 5-6 big cloves) Sautee on low for 5-10 mins.
Add 1 cup cooked rice and stir in sauce, enough to cover all of meat and rice, about a cup (you don't want it to be too watery)and cook on low until sauce is warmed up.
Fill peppers with stuffing and place in ungreased baking dish (I use 9x13x2 Pyrex). Pour remaining sauce over peppers. Cover and bake in oven at 350 for 45 mins.
Remove cover and sprinkle shredded mozzarella on top of peppers and bake at 350 for another 15 mins.
Serve with Pasta and Garlic Bread!