Arrange chicken pieces in a single layer in an ungreased 13"x9" baking pan; set aside. Combine soy sauce, ginger, pepper, onion, brown sugar, reserved pineapple juice and orange juice; pour over chicken. Cover and refrigerate one hour or overnight, turning once.
Bake, covered, at 350° for 30 minutes or until tender. Uncover, and bake 20 to 25 more minutes or until golden and juices run clear when chicken is pierced with a fork. Remove chicken from baking pan; keep warm on a platter.
Skim off fat from pan drippings. In a medium saucepan, combine cornstarch and water with pan juices; heat until thickened and bubbly. Stir in pineapple and oranges and warm through; pour over chicken. Serve with cooked rice.