Preheat oven to 350 degrees F (175 degrees C). In a large skillet, brown ground beef and sausage. Mix onion into the sausage and beef mixture, and saute it until tender. Drain grease out of skillet. Stir processed cheese food into the mixture. Continue cooking until cheese melts. Arrange slices of bread on a cookie sheet, place heaping spoonfuls of the mixture onto each slice of bread. Bake 12 to 15 minutes.
