In a large zip baggie, combine the taco seasoning, tomato juice and oil. Swish around to mix well. Pour our ½ cup into a dish to set aside for basting later. Add the chicken to the bag, and move it around to coat with the marinade. Zip the baggie closed, and refrigerate to let marinate for at least 3 hours.
Drain and discard the marinade from the chicken. On six metal skewers, alternately thread the chicken, peppers, onion and tomatoes. Grill, uncovered, over medium-heat for 3 minutes on each side. Baste with the reserved marinade. Continue turning and basting until the chicken is cooked through, 6 to 8 minutes. Serve with salsa, sour cream and/or guacamole.