1. Heat a grill to high (450° to 550°). Mix mustard, Worcestershire, vinegar, salt, and pepper in a medium bowl. Add steak, tossing to coat.
2. Grill steak, turning once halfway through, until done the way you like, 6 to 8 minutes for medium. Let rest, covered with foil, 10 minutes before slicing.
3. Put remaining ingredients in a large bowl and toss gently to combine. Divide salad among 4 plates and serve steak over salad.