In small bowl, mix dressing ingredients using wire whisk until well blended. Cover; refrigerate until ready to use.
Cook and drain pasta as directed on package. Rinse with cold water; drain.
In large bowl, mix cooked pasta, chicken, spinach, grapes and celery. Stir dressing; pour over salad and toss gently to coat. Refrigerate at least one hour before serving. Stir in almonds, reserving 2 tablespoons for garnish, if desired.