Combine 1/4 cup Wish-Bone® Robusto Italian Dressing with steak in large resealable plastic bag; turn to coat. Combine additional 1/4 cup Dressing, green pepper, onion and mushrooms in another large resealable plastic bag; turn to coat. Close bags and marinate in refrigerator, turning occasionally, at least 2 hours.
Remove steak and vegetables from marinades, discarding marinades. Grill or broil steak and vegetables, turning once, 6 minutes or until steak is desired doneness. Slice steak and vegetables.
Toss salad greens with remaining 1/2 cup Dressing in serving bowl, then top with steak and vegetables.