Cook pasta according to package directions. Run cool water over pasta and drain.
Into a large bowl, add the drained pasta, red grapes, celery, almonds, green onions, and chicken.
For the dressing, roughly chop the fresh tarragon and place it in a high powered blender. Add the remaining dressing ingredients. Blend on high power for 30 seconds, or until dressing is smooth and frothy.
Add half of the dressing to the bowl with the salad ingredients and stir to combine.
Cover the salad and the remaining half of the dressing and chill for 1-2 hours. Pour the rest of the dressing over the salad just before serving.