Hamburgers are customarily eaten as a sandwich, between two halves of a round bun. mustard, mayonnaise, ketchup, and other condiments, along with garnishes of lettuce, onion, tomato, and sliced pickle, constitute the customary dressing.fried eggs and avocado may be added as well. In the variation known as the cheeseburger, a slice of cheese is melted over the patty. Learn more