Pat the chicken dry very well and remove any excess fat or skin, if necessary.
In medium sized pot, add the shoyu, water, brown sugar, sliced ginger, chopped garlic and green onion and stir to combine. This is a good time to taste and adjust as needed.
Add the chicken to the shoyu mixture and bring up to a low boil. Continue cooking the chicken for 35-45 minutes, until the chicken is cooked through and tender.
Once the chicken is done, remove to a foil lined baking sheet and place chicken skin side up.
Place the chicken under the broiler for 2-3 minutes to crisp up the skin. Keep an eye on it and make sure it's not burning too quickly.
Meanwhile, if shoyu sauce is thin, whisk cornstarch and some of the hot shoyu broth in a bowl and add back to the shoyu mixture. Continue cooking on a simmer until the sauce slightly thickens.
Once the chicken is done, plate the chicken on top of cooked white rice and spoon thickened shoyu sauce on top of the chicken. Garnish with chopped green onions and serve.