Sprinkle meat with meat tenderizer. Place in a shallow glass baking dish large enough to accommodate the meat. Mix together onion, garlic, vinegar, oil, Worcestershire sauce, and chili powder, and pour over steak. Marinate for 2 or more hours in the refrigerator.

Preheat grill for medium-low heat.

Brush grate with oil. Transfer steak to grill, reserving marinade. Cook, covered, for 30 to 40 minutes, or to your desired degree of doneness, turning once. Allow steak to rest for a few minutes off the heat.

While meat is cooking prepare sauce. Combine reserved marinade, tomato sauce, lemon slices, brown sugar, mustard powder, and hot sauce in a medium saucepan. Simmer for 10 minutes over medium low heat.

Slice meat across the grain. Spoon sauce over steak, and serve.