Substitute sherry vinegar for the red wine vinegar and walnut oil for the canola oil if you like.
Heat oven to 350° F. Place the walnuts on an ungreased cookie sheet and toast until lightly browned, about 5 to 7 minutes, stirring occasionally. Remove and let cool.
In a large bowl, combine the oil, vinegar, and mustard. Whisk together to combine well and season to taste with salt and groun pepper. Add the endives, watercress, and toasted walnuts and toss to mix well. Serve immediately.