The ingredients for this colorful salad can be prepared in advance and stored in separate containers, leaving only the arrangement for the last minute.
Scatter shredded lettuce on a serving platter. Arrange vegetables, radicchio, endive, and cheese in separate rows on top of lettuce.
Whisk together mustard, vinegar, salt, and pepper. Slowly whisk in olive oil. Drizzle dressing over salad, sprinkle with parsley and watercress or mache leaves, add more pepper, and serve.