Cut a small piece off the curved side of 4 unpeeled bananas so they'll sit level, then make a deep slit down the center of each through the peel; place on separate sheets of foil. Open the slits and brush the inside of each banana with melted butter, then sprinkle with sugar and the semisweet chocolate chips; fold up the foil. Grill the packets over high heat until the chocolate melts, 5 to 8 minutes (don't worry if the peel turns brown). Open the peels and top the bananas with ice cream, whipped cream, sprinkles and a cherry. Serve right in the foil packets.