For the Dressing: Combine the yogurt, mayonnaise, lemon juice, salt, pepper, and poppy seeds in a small mixing bowl; mix well.
For the Pasta Salad: Cook the pasta according to the package directions; drain and rinse under cold water. Combine the pasta, chicken, mandarin oranges, green onion, and celery in a large bowl. Add the dressing; toss to coat. Cover and refrigerate until time to serve.
Nutritional Information Per Serving: Calories 330; Total fat 9g; Saturated fat 2.5g; Cholesterol 40mg; Sodium 460mg; Carbohydrate 37g; Fiber 2g; Protein 26g; Vitamin A 20%DV*; Vitamin C 40%DV; Calcium 15%DV; Iron 15%DV; Folate 21%DV; Potassium 12%DV