Cut tomato and onion into slices - depending on how much you like them, add as much as you like!
Take a non stick frying pan. Add onions and first brown them off until soft, then add the sugar and cinnamon. Fry on a high heat for about a minute or so. Add the tomatoes at the very last minute just to brown slightly in the caramel.
Toast your bread on one side, then place the cheese (again, however much you like) and place under the grill until melted. Add the onions and tomatoes; place under the grill for about 2 minutes and Voila! it's done and ready to eat!
Toast one side of you bread while caramelising to cut down on the time.