Remove and discard stems from mushrooms; slice mushrooms.
Sprinkle steak with pepper and salt; coat with cooking spray. Heat a large nonstick skillet over high heat. Add beef; cook 3 to 4 minutes on each side or until desired degree of doneness. Place beef on a platter; keep warm.
Heat oil in pan over medium heat until hot; add shallots, and sauté 1 minute. Add sliced mushrooms; sauté 4 minutes or until tender. Add wine; bring to a boil, reduce heat, and simmer 2 minutes.
Add broth and Dijon mustard; boil 5 minutes or until liquid is reduced by half. Remove from heat. Add butter; stir until butter melts. Spoon sauce over beef.