Light a grill. Lightly brush the grate with oil and arrange the chicken breasts on the grate, skin side down, with the breast tips facing in the same direction at a 45° angle to the bars of the grate. Set a large cast-iron skillet on top of the breasts and grill over a medium-hot fire for 8 minutes; rotate the chicken breasts a quarter turn after 4 minutes to make attractive crosshatched grill marks. Flip the chicken breasts and repeat, grilling them until they are cooked through, about 8 minutes longer. Serve with lemon wedges.