Cut bananas in half lengthwise. Melt butter in a nonstick skillet over medium-high heat. Add brown sugar and lay the banana slices on top, cut side up. Cook undisturbed for 20 seconds, then add rum (or orange juice) and cinnamon. Cook for 10 seconds, then turn bananas carefully and cook for 45 to 60 seconds more, basting with the pan sauce. Divide the bananas between 2 dessert plates, drizzling the sauce on top. Serve immediately, with a scoop of ice cream (or frozen yogurt).