Cut a small piece off the curved side of 4 unpeeled bananas so they can sit flat, then make a deep slit down the center of the other side through the peel. Place each on a sheet of foil. Open the slits and brush the bananas with melted butter, then sprinkle with sugar and stuff each with 1 ounce chopped semisweet chocolate. Fold in the sides of the foil and seal to form a packet. Grill over high heat until the chocolate melts, 6 to 8 minutes. To serve, open the peels and top with chocolate ice cream, whipped cream, nuts and a maraschino cherry.