Wash and halve peppers lengthwise, removing veins and seeds. Steam lightly and set aside. Cook cous-cous in water for 2-3 minutes; let stand for 10 minutes, then add butter, chopped tomato and chopped scallions. Mix well, salt to taste. Stuff cous-cous mixture in pepper halves. Covver each pepper with a slice of cheese, sprinkle sesame seeds on top and place in warm oven until cheese melts.