Bring a large pot of lightly salted water to a boil. Add pasta and cook for 8 to 10 minutes or until al dente; drain and set aside.
In a medium bowl whisk together coleslaw dressing and mayonnaise.
In a large bowl combine pasta, chicken, green grapes, red grapes, water chestnuts, celery and spring onions. Stir in dressing and mix well. Place the salad in the refrigerator to marinate for 2 hours or overnight. Mix in cashews and dried cranberries just before serving. Serve cold.