In a shallow baking pan large enough to hold bananas in one layer stir together butter and brown sugar and add bananas, tossing gently to coat.
Transfer bananas with a metal spatula to an oiled grill pan and grill until browned and cooked through, about 2 minutes on each side (if bananas are difficult to handle you may grill them on 1 side only).
In a heavy saucepan chopped chocolate, cinnamon and half and half over low heat, stirring frequently, until chocolate is melted.