Prepare and cook potatoes; cool slightly. Cut into cubes (about 6 cups). Mix mayonnaise, vinegar, mustard, salt and pepper in large glass or plastic bowl. Add potatoes, celery and onion; toss. Stir in chilies. Cover and refrigerate at least 4 hours. Before serving stir in avocados and tomatoes. 10 Servings (About 3/4 Cup Each); 400 Calories Per Serving.