Preheat a grill to medium high. Top a honey graham-cracker square with a 1/2-to-1-ounce square of semisweet chocolate. Place on the edge of the grill, away from the direct heat, to melt the chocolate. Meanwhile, skewer a jumbo marshmallow and hold over the heat, turning, until soft and toasted. Put the marshmallow on top of the chocolate, cover with another graham and gently press together as you slide off the skewer.