Pour ½ cup dressing over steak in large, shallow nonaluminum baking dish or plastic bag. Cover or close bag and marinate in refrigerator, turning occasionally, 30 minutes or up to 3 hours. Grill or broil steak and zucchini, turning once, brushing frequently with an additional ¼ cup dressing, until steak is done and zucchini is tender. Let rest; thinly slice steak and cut up zucchini.
Arrange lettuce on platter with avocado, radishes, carrots, steak and zucchini. Drizzle with remaining dressing and sprinkle with pumpkin seeds.