In a large bowl, combine soy sauce, brown sugar, dark soy sauce, and ginger. Add chicken, toss to coat, cover, and chill for at least 1 hour and up to overnight.
Preheat oven to 375°. Lay out 8 pieces of aluminum foil, 6 to 8 in. long each. Put 1/8 of the marinated chicken in the middle of each. Top chicken with green onions and sprinkle with pepper. Fold 1 side of foil over the chicken to cover it, fold opposite side of foil over first fold, and then fold in each end once to seal and create a little packet.
Lay packets on a foil- or parchment-lined rimmed baking sheet (packets will leak while cooking, and the marinade is difficult to clean up once it cooks onto a pan). Bake until chicken is cooked through and marinade is reduced and starting to caramelize in each packet, 45 to 60 minutes. Serve hot or warm.
Note: Nutritional analysis is per serving.