Preheat a grill to high. Pierce the steak in a few spots with a fork and season with salt and pepper. Mix the Worcestershire sauce and 1 tablespoon olive oil in a large bowl; add the steak and turn to coat. Grill the steak until marked on both sides and a thermometer inserted sideways into the center registers 125 degrees F, about 7 minutes per side. Transfer to a cutting board and let rest 5 to 10 minutes.
Meanwhile, cook the barley as the label directs, then remove from the heat. Stir in the carrots, celery, spinach, mushrooms and scallions; cover and set aside.
Whisk the lemon zest and juice, the mustard and the remaining 2 tablespoons olive oil in a bowl. Add the barley mixture and toss. Season with salt and pepper.
Thinly slice the steak against the grain and season with salt and pepper. Divide among plates and serve with the barley salad.
Per serving: Calories 436; Fat 17 g (Saturated 4 g); Cholesterol 58 mg; Sodium 358 mg; Carbohydrate 37 g; Fiber 6 g; Protein 36 g