Thinly sice the chicken breast diagonally so that it will cook though quickly. Grate the ginger.
Put the ginger, mentsuyu sauce and chicken in a plastic bag. Close the bag up with one hand, and rub the chicken over the bag firmly with the other hand.
Marinade in the refrigerator for at least 30 minutes. (I leave it for an hour.)
Add a little less water than indicated on the package to the tempura flour to make a slightly stiff batter. Coat the chicken pieces in the batter.
Deep fry in oil. Since the chicken is sliced so thin, it will fry quickly.
Story Behind this Recipe
I used store-bought mentsuyu sauce to season the chicken before cooking and was surprised that inexpensive chicken breast becomes tender and delicious. If you use 3x concentrate mentsuyu, you won't need dipping sauce.
Slice the chicken breast thinly on the diagonal. I recommend not omitting the ginger.