Turn on the oven broiler to high. Put the rack 10cm from the heat. Put the olive oil in a non-stick fry-pan on medium heat. Add the leftover spaghetti. Turn with a wooden spoon until the spaghetti is warmed. Pour on the eggs and cook for 30 seconds. Sprinkle the cheese over and slide the pan under the broiler. Broil until the eggs are firm and the frittata is lightly browned on top. Slice out onto on to a plate. To serve pile a few slices of the frittata on your favorite bread.