Bring a large pot of lightly salted water to a boil.
Add pasta, and cook for 8 to 10 minutes or until al dente. Rinse with cold water, drain, and set aside.
In a large bowl, whisk together oil, orange juice, vinegar, salt, and orange zest. Stir in cooked chicken until coated. Stir in cooked orzo, cantaloupe, grape halves, and mayonnaise. Cover and chill for 4 to 6 hours. Just before serving, stir in cashews.