Trim fat from steak and set aside. Combine bell pepper pieces, tomato halves, 1 tbs lime juice, 1 tbs worchestershire sauce, 1/4 tsp salt and half of minced garlic in a large bowl. Toss gently and set aside. Combine remaining lime juice and worchestershire, 1/4 tsp salt, remaining minced garlic and flank steak in a large zip top plastic bag; seal bag and marinate in refrigerator at least 30 minutes. Remove steak from bag, reserving marinade. Rub chili powder evenly over steak, and set aside. Remove bell pepper pieces and tomato halves from bowl, reserving marinade. Set tomatoes aside. Prepare grill. Place seak, pepper pieces, tomato halves and onion slices on grill rack coated with cooking spray. Grill tomato halves 3 minutes on each side. Grill steak five minutes on each side or until desired degree of doneness, basting occasionally with reserved marinade. Grill bell pepper pieces and onions six minutes on each side or until tender, basting occasionally with reserved marinade. remove steak and vegetables from grill. Let steak stand five minutes; cut steak diagonally across grain into thin slices. Cut bell pepper pieces into 1/4 inch slices and cut onion slices in half. Sprinkle remaining 1/4 tsp salt over vegetables. Heat flour tortillas according to package directions. Place two tortillas on each of four plates. Divide steak, bell pepper and onion evenly amoung tortillas. Top each fajita with 1/2 tomatoe and 1/12 tsp fat free sour cream. Serve warm