One day before making the empanadas, boil the plantains, in their skins, until the skins begin to crack and the meat is soft, about half an hour. Allow to cool; cover and refrigerate.
Preheat oven to 375 degrees. To make the empanadas, peel and mash the cooled plantains in a food processor, fully breaking down the fruit, to form the dough. Roll into 8-10 balls slightly bigger than a walnut. With a tortilla press or rolling pin (and the dough sandwiched between a folded sheet of plastic wrap), form flat circles of dough about 1/4 inch thick. On one half of the dough, drop about a tablespoon full of refried beans. Using the plastic wrap, fold the dough to cover the beans and crimp sides to seal.
Place formed empanadas on a greased cookie sheet. Spritz with a little vegetable spray and bake until the tops begin to brown and the filling is hot, about 17-20 minutes. Serve hot with a salsa of your choice.