Mix all the ingredients for the marinade in a bowl.
Cut the steak into thin strips, about 5 x 2.5 cm/2 x 1 inches. Place the steak in the marinade and turn to coat the meat, then leave for about 30 minutes.
Meanwhile, put the black beans in a bowl of cold water and leave for about 15 minutes. Drain the beans and rinse well, then add the sugar and mash