Preheat oven to 325 °F.
Arrange chicken pieces in a baking dish. Mix remaining ingredients except green onion together. Pour over chicken. Cover tightly and bake for 45 min to 1 hour or until chicken tests done.
Chicken can be served as is, sprinkled with green onion. Optionally, the chicken can be removed, the cooking liquid thickened with a cornstarch slurry, and then poured over the chicken.
Mirin is sweet, Japanese cooking wine. You can substitute with Chinese rice wine plus 1 tsp sugar.
If avoiding wheat/gluten, be sure to use wheat/gluten free tamari/soy sauce, ponzu, and oyster sauce.
To avoid seafood, omit oyster sauce. My research has found that Lee Kum Kee Panda Brand Green Label oyster sauce is gluten-free.
Ponzu sauce is a slightly sweetened blend of soy sauce and citrus juice. To substitute, use 1 Tbsp soy sauce plus 1 Tbsp lime juice plus 1/2 tsp sugar. My research has found that Wan Ja Shan makes a gluten-free organic ponzu sauce.
If avoiding corn, omit thickening the sauce or use an alternative thickener such as arrowroot or tapioca starch.