Sprinkle steak generously on both sides with meat tenderizer; let stand 1/2 hour or more. In a shallow glass dish, combine oil, catsup, vinegar, and Worcestershire sauce; mix well. Place steak in marinade. Spread onion over steak. If marinade does not cover steak, turn or baste often. Let steak marinate for 3 to 4 hours or longer. Soak a double handful of hickory chips in water while charcoal fire is heating. When fire is hot, toss the soaked hickory chips on the fire. Place meat on grill about 3 inches above fire. To keep flame down, sprinkle fire with water. (We use a sponge.) Cook about 8 minutes on each side, or until desired doneness. Use a sharp knife to carve, cutting diagonally across grain of meat into very thin slices. If hickory chips are not available, the meat will still be delicious.