Preheat broiler. Diagonally cut 6 (1/2-inch) thick slices from bread, reserving remainder for another use. Grate the cheese.
On a baking sheet, toast both sides of the bread slices under the broiler about 4 inches from heat, leaving the broiler on. Rub the toast with garlic. Top toasts with cheese and broil until cheese is just melted, about 2 minutes.