Mix mayonnaise, lemon peel, and fresh lemon juice in medium bowl to blend. Season to taste with salt and pepper. Refrigerate 15 minutes. Toss apples, celery, radishes, cranberries, and red onion in large bowl. Add lemon mayonnaise and toss to coat. (Can be prepared up to 8 hours ahead. Cover and refrigerate.) Fold watercress and pecans into salad. Arrange 2 radicchio leaves on each plate. Spoon salad into center of radicchio leaves and serve.