A cheeseburger is a hamburger topped with cheese. Traditionally, the slice of cheese is placed on top of the meat patty, but the burger can include variations in structure, ingredients and composition. The cheese is usually added to the cooking hamburger patty shortly before serving so it melts.
An onion ring is a form of appetizer or side dish. They generally consist of a cross-sectional "ring" of onion dipped in batter or bread crumbs and then deep fried. The cooking process decomposes propanethial oxide in the onion into the sweet-smelling and tasting bispropenyl disulfide.