Heat grill to medium heat.
Combine first 4 ingredients. Add half the cheese mixture to meat; mix just until blended. Shape into 4 (1/2-inch-thick) patties.
Grill 4 to 5 min. on each side or until done (160ºF), adding buns, cut sides down, to the grill to toast for the last few minutes.
Place burgers on bottom halves of buns; top with remaining cheese mixture. Cover with top halves of buns.