Shape beef into 6 (1/2 inch thick) patties. Sprinkle with garlic powder, salt and pepper. Place patties on grill; cover grill. Cook with medium heat 8 to 10 minutes, turning once, until meat thermometer inserted in center of patties reads 160°F. Place cheese slices on top of burgers; cover and cook 1 to 2 minutes longer or until cheese is melted.