1-pound flank steak, all visible fat removed
2 teaspoons coarsely cracked black pepper
Vegetable oil spray
1 cup (about 3 ounces) sliced fresh mushrooms
2 green onions, sliced
1/2 teaspoon bottled minced garlic
1 tablespoon all-purpose flour
1 cup evaporated skim milk or skim milk
2 teaspoons Dijon mustard
To prevent meat from curling as it cooks, make 6 shallow slashes on each side of the meat in a crisscross fashion (three slashes in each direction).
Rub cracked pepper onto each side of the steak. Place steak on the unheated rack of a broiler pan. Broil 3 to 5 inches from the heat for 3 to 5 minutes. Turn and broil meat about 5 minutes more, or until desired doneness.
Meanwhile, spray a medium saucepan with vegetable oil. Place over medium heat. Cook mushrooms, green onions and garlic in skillet until mushrooms are just tender, about 5 minutes. Stir in flour. Add milk and mustard all at once. Cook and stir until thickened and bubbly, about 3 minutes. Cook 2 minutes more, stirring constantly.
To serve, thinly slice steak diagonally across the grain. Serve with mustard sauce.