Cut capsicums in half, place them in a 20x30cm baking dish and set aside. In a large frypan over medium heat, saute the beef mince for 5 minutes. Add 1 1/2 cups chopped onion, chopped green capsicum and garlic. Reduce heat to low, add pasta sauce and let simmer while preparing the couscous.
Prepare couscous according to packet directions, but add the remaining onion to the water before adding the couscous. When couscous is done, combine it with the sauce. Fill capsicums with the mixture. Top each with grated cheese.
Bake at 190 degrees C for 20 minutes or until cheese is bubbly and slightly brown on top.