Adding cheese to a burger after the fact is a cardinal sin! You'd be better leaving it off than deciding to eat a burger with cold, hard cheese on it. Also, be choosy about your fromage choices. Those with a good melting point are your best bets as well as creamy, spreadable options such as Boursin or soft goat's cheese. Or you can keep things classic with a slice of good ol' American cheese, slapped onto your patties just 2 minutes before you're done grilling.