Cut peppers in half, place them in a 9x13 inch baking dish, and set aside. In a large skillet over medium heat, saute the ground beef for 5 minutes.
Add 1 1/2 cups chopped onion, chopped green bell pepper, and garlic. Reduce heat to low, add tomato sauce, and let simmer while preparing the couscous.
Prepare couscous according to package directions, but add the remaining onion to the water before adding the couscous. When couscous is done, combine it with the sauce. Fill bell peppers with the mixture. Top each with shredded cheese.
Bake at 375 degrees F (190 degrees C) for 20 minutes, or until cheese is bubbly and slightly brown on top.
