In a jar with a tight-fitting lid, combine the first six ingredients; shake well. Refrigerate until serving.
In a small bowl, combine marinade ingredients. Brush on both sides of steak; let stand for 30 minutes. Broil steak 4 in. from the heat for 5-6 minutes on each side or until meat reaches desired doneness.
Meanwhile, on two plates, arrange greens, tomato, avocado and onion. Thinly slice steak; place on top of salads. Serve with dressing. Yield: 2 servings.