In a large skillet over medium-high heat, saute steak and onion in oil until steak is no longer pink; drain. Stir in steak sauce. Arrange tortilla chips on a large oven-proof platter or baking sheet. Spoon steak mixture over chips; sprinkle with cheese. Broil 6 inches from heat source for 3-5 minutes or until cheese melts. Top with tomatoes, chilies, and olives. Serve immediatley, with sour cream if desired.