Cut each plantain into 4 equal parts including skin. In sauce pan bring water and salt to boil, add plantain and cook until soft, about 10 minutes. Drain.
Peel plantain, discard skin. Mash plantain until smooth using food processor or hand masher.
Put about 3 tbsp. of mashed plantain between two pieces of plastic wrap. Use a rolling pin and/or your hands to shape the empanada and make a 4 ½ inch circle about ¼ inch thick. Put 1 ½ tbsp. of refried beans on empanada and, using plastic wrap to lift, fold it over to form a half. Using your fingers, seal the edge of empanada. Repeat using all the plantain mixture. You should have about 6 empanadas.
In shallow bowl combine sugar and cinnamon. Set aside.
In skillet heat ½ inch oil on medium. Oil should be hot, but not smoking, about 350° F. Fry the empanadas until lightly browned on both sides. Drain on paper towels.
While still warm, dredge empanadas in sugar to coat on both sides. Serve warm.