In a blender or food processor, combine the yogurt, mayonnaise, oil, vinegar and onion. Puree until smooth. Add the celery seed, black pepper, cayenne, salt and sugar and pulse a couple of times to blend. In a large salad bowl, combine the slaw ingredients. Add the dressing and mix well. Chill. Just before serving, sprinkle in the peanuts or pecans.
Makes about 12 servings