Wash chicken, pat dry and set aside. Make marinade: In a large bowl, combine balsamic vinegar, soy sauce, honey, brown mustard, garlic and green onions. Whisk to thoroughly combine. Reserve 1/4 cup marinade for basting chicken. Place chicken in a glass baking dish. Pour marinade over chicken and turn pieces to coat all sides. Cover and refrigerate for several hours or overnight. When ready to cook, heat grill or skillet. Cook chicken until internal temperature reaches 165 degrees or until chicken is thoroughly cooked. Baste chicken with reserved marinade as needed for added liquid and to give the chicken a glazed finish. Do not burn outside of chicken. If skin begins to burn, lower heat. Garnish with thin sliced green onions.