HEAT grill to medium-high heat.
CHOP 2 chiles; mix with meat and garlic. Shape into 6 patties.
GRILL patties and onions 4 to 6 min. on each side or until patties are done (160ºF). Meanwhile, cut remaining chiles into strips. Top burgers with Singles; grill until Singles are melted.
SPREAD buns with mayo; fill with cheeseburgers, chili strips and onions, separated into rings.