Grill or broil the sirloin steak to desired doneness, preferably rare or medium rare. When cool, trim off fat and slice thinly.
Cut the French baguette into at least 24 1/4 inch slices. Brush both sides of each toast with olive oil. Place toasts on a baking sheet under the broiler until golden on both sides.
Spread Stonewall Kitchen Blue Cheese Herb Mustard over each French bread toast. Then layer a piece of steak. Top each crostini with crumbled blue cheese and a parsley leaf for garnish. Serve at room temperature.