Heat oven to 450°F. Line a baking pan with foil. Crush 1/3 of the box of croutons in food processor. Brush tenderloin with mustard, then pat crouton crumbs onto top and sides of tenderloin and place in baking pan. Coat pork with vegetable cooking spray.
Bake 25 to 30 minutes, or until meat thermometer registers 160°F. Let rest 5 minutes before slicing.
Prepare dressing mix according to package directions. Toss 3 tablespoons of dressing with salad greens, cherry tomatoes, and remaining croutons.