Heat grill to medium heat.
Shape meat into 6 (1/2-inch-thick) patties.
Grill 6 to 8 min. on each side or until done (160°F). Top with Singles; grill 1 min. or until melted.
Place lettuce on bottom halves of buns; top with tomatoes, cheeseburgers, pickles and ketchup. Cover with tops of buns.