1. In a small bowl, stir together the chili powder, garlic salt, cumin and sugar until well blended. Stir in the Worcestershire sauce until well blended.
2. In another small bowl, stir together the oil and 1 teaspoon of the Worcestershire-chili mixture; set the oil mixture aside.
3. Brush the meat with the remaining Worcestershire-chili mixture. Place the meat in a glass baking dish; cover the dish and refrigerate for 1 to 2 hours for the meat to marinate.
4. Prepare an outdoor grill with hot coals, or heat gas grill to high, or see the Broiler Method, below.
5. Lightly brush the grill grid with vegetable oil. Place the meat on the grill grid. Cover the grill. Cook the meat for 5 minutes. Uncover the grill. Turn the meat over; re-cover the grill. Cook for another 5 to 7 minutes or until an instant-read thermometer inserted in the meat in its thickest part registers 140 degrees F (temperature of the meat will rise another 5 to 10 degrees for medium-rare while the meat is standing; cook meat longer for medium or more doneness). Let meat stand in warm place for 10 minutes before slicing.
6. Brush the tops of the mushrooms with the reserved oil-Worcestershire-chili mixture.
7. Grill the mushrooms, top side down, uncovered, until lightly colored, 2 to 3 minutes. Turn the mushrooms over; grill until fork-tender, about another 5 minutes.
8. To serve, thinly slice the meat against grain. Serve the meat warm, sprinkled with black pepper, if desired, and with the grilled mushrooms, sprinkled with fresh lemon juice, if desired. Makes 6 servings.