In a large resealable plastic bag, combine the vinegar, lime juice, 1 tablespoon oil, Worcestershire sauce, onion, garlic, salt if desired, oregano and cumin; add chicken. Seal bag and turn to coat; refrigerate at least 4 hours.
Drain and discard marinade from chicken. Using long-handled tongs, moisten a paper towel with cooking oil and lightly coat the grill rack. Lightly brush vegetables with remaining canola oil. Grill vegetables and chicken, covered, over medium heat or broil 4 in. from the grill for 12-15 minutes or until a thermometer reaches 170°
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. Serve with salsa, guacamole, sour cream and/or cheese if desired.
Grilled Beef Fajitas: Prepare as directed, using 1-1/2 pounds beef flank steak in place of the chicken. Grill over medium heat for 6 to 8 minutes on each side or until meat reaches desired doneness (for medium-rare, a meat thermometer should read 145°; medium, 160°; well-done, 170°).