Light a grill or heat a grill pan. Set the turkey skin side down on a work surface. With the knife parallel to the work surface, cut through the breast, leaving 1 inch of meat attached at one side, then open it up like a book; the goal is to have meat that is of even thickness. Season with salt and pepper. Grill the turkey over moderate heat, turning once, until the skin is crisp and the meat is just cooked through, about 25 minutes.