Heat grill. Sprinkle both sides of beef steak with garlic-pepper blend and salt. On 18x12-inch sheet of heavy-duty foil, combine mushrooms, onions and roasted peppers. Wrap securely with double-fold seals.
When ready to grill, place mushroom packet and steak on gas grill over medium-high heat or on charcoal grill 4 to 6 inches from medium-high coals. Cook 10 to 15 minutes or until steak is of desired doneness, turning once, and mushroom mixture in packet is thoroughly heated.
To serve, cut steak into serving-sized pieces. Open mushroom packet carefully to allow steam to escape. Top each steak serving with mushroom mixture.