Cut off the nerves of the chicken. Cut the chicken in cubes, into pieces of the same size. Put the chicken pieces in a bowl.
Mix the soy sauce, mirin and the piece of ginger in a jar, spread this mix over the chicken; make sure the chicken cubes are well covered with the marinade. Let it stand for 15 minutes, and slip of the excess of marinade.
Mix the nori with the cornstarch, and with your fingertips, coat lightly each chicken cube with the mix. Heat the oil in a heavy skillet at medium heat. Fry 6 or 7 chicken pieces at the same time until they are golden, turning them from time to time. Put the chicken pieces on absorbent paper.
Serve with cooked steamed rice, pickled ginger (gari) and cucumber slices.