In a large resealable plastic bag, combine the vinegar, lime juice, oil, Worcestershire sauce, onion, garlic, salt if desired, oregano and cumin. Add chicken. Seal and refrigerate for at least 4 hours.
Discard marinade. Lightly oil vegetables. Grill vegetables and chicken, uncovered, over medium heat for 12-15 minutes or until vegetables begin to soften and chicken juices run clear.
Meanwhile, warm tortillas according to package directions. Quickly slice chicken and peppers into strips and separate onion slices into rings. Spoon chicken and vegetables down the center of tortillas; fold in sides. Garnish as desired with salsa, guacamole, sour cream and cheese. Yield: 6 servings.