Combine first 8 ingredients in a jar; cover tightly, and shake vigorously. Chill thoroughly.
Snap off tough ends of asparagus. Remove scales from stalks with a knife or vegetable peeler, if desired. Arrange asparagus in a vegetable steamer over boiling water. Cover and steam 4 to 5 minutes or until crisp-tender. Drain; let cool to room temperature.
Arrange asparagus, squash, and tomato on 2 watercress-lined salad plates. Sprinkle evenly with cheese. Drizzle vinegar mixture evenly over salads.