In a large skillet, heat oil over medium heat. Add chicken; cook until golden brown, 8-10 minutes on each side. In a small bowl, whisk water, brown sugar, orange juice, soy sauce, ketchup, vinegar, garlic, pepper flakes and five-spice powder. Pour over chicken. Bring to a boil. Reduce heat; simmer, uncovered, until chicken is tender, 30-35 minutes, turning chicken occasionally., In a small bowl, mix cornstarch and cold water until smooth; stir into pan. Bring to a boil; cook and stir until sauce is thickened, about 1 minute. Sprinkle with green onions. If desired, serve with rice. Freeze option: Cool chicken. Freeze in freezer containers. To use, partially thaw in refrigerator overnight. Heat slowly in a covered skillet until a thermometer inserted in chicken reads 165°, stirring occasionally and adding a little water if necessary.