If you don't have a ring mold, divide the lamb mixture into 8 equal-sized patties, about 4 inches across. Place about 1 tablespoon of each cheese on top of a patty, and place another patty on top. Pinch the sides of the 2 patties together so they form one larger patty. Repeat with the remaining patties to create 3 more. Cover the patties in plastic wrap and refrigerate for about an hour.