Bring 2-3 quarts of water to a rolling boil; add pasta, stir, and cook 9-12 minutes or until al dente. Drain and rinse under cold running water until chilled; transfer pasta to a large bowl.
To the bowl, add the diced chicken and grapes; toss. Add the yogurt, mayonnaise, and salt sprinkled over the top. Mix the pasta well, incorporating the mayonnaise and yogurt well. Fold in the cashews. serve immediately, chilled, or refrigerate for up to 5 days.