Place steaks, mushrooms, onion, and tomatoes on the rack of the grill directly over medium heat. Grill steaks until desired doneness, turning once. (Allow 11 to 15 minutes for medium-rare doneness [145 degrees F] or 14 to 18 minutes for medium doneness [160 degrees F].) Grill mushrooms, onion, and tomatoes until tender, turning once halfway through grilling. (Allow 10 minutes for mushrooms, 15 minutes for onion, and 7 minutes for tomatoes.) Remove vegetables and steaks from grill as they are done.