Peel the bananas and halve them lengthwise. In a chafing dish, over medium flame, melt the butter with the brown sugar. Stir in the lemon juice and add the bananas. Saute until bananas are tender (2 minutes). Sprinkle on cinnamon. Slowly pour the warmed rum over the bananas and light with match. The flame can be too high so pay attention. Keep spooning rum until flames are extinguished. Immediately spoon banana halves, with their sauce, around a scoop of ice cream. Serves 4.