To prepare dressing, place first 11 ingredients in a blender or food processor; process until smooth. Chill.
To prepare salad, combine lettuce and watercress in a large bowl. Place 2 cups lettuce mixture on each of 4 plates. Arrange 6 tablespoons chicken, 4 tomato wedges, 2 egg wedges, 2 tablespoons avocado, and 1 tablespoon cheese over each serving. Serve each salad with 1/4 cup dressing.