In a bowl, combine pears, celery, grapes, and walnuts. In another bowl, combine yogurt, mayonnaise, and poppy seed; mix well and add to pear mixture. Toss to coat. Refrigerate for one hour. To serve, place 4 tablespoons of pear mixture on each tortilla. Tortilla may be cut in half before serving.
Yield: 5 to 10 servings.