Melt the butter in a heavy skillet over medium-high heat. Add the brown sugar. Stir together and cook for 2 minutes.
Drop banana slices into the pan. Cook for about 3-5 minutes, until they begin to brown slightly. Pour in the cream and stir to combine. Add the chopped nuts and stir into the sauce. Carefully add the rum. Stir in the cinnamon and toss to coat.