Combine beef and mushrooms in a small bowl or plastic bag. Add garlic to vinaigrette. Pour half of the vinaigrette over beef and mushrooms and toss until well coated. Cover and marinate at room temperature for 30 minutes or in the refrigerator for up to 24 hours.
Arrange lettuce leaves on a plate. Top with beef and mushrooms, radishes, tomatoes, broccoli, and green onion. Drizzle remaining vinaigrette over vegetables. Makes 1 serving.