Chop, chop, chop the veg - Chop the celery into a dice; rinse and chop the preserved lemon (peel only); finely chop the tarragon and the scallions.
Steam and chop the shrimp - Steam the shrimp for 4 minutes, then transfer to a strainer and rinse in cool water to stop the cooking. Drain thoroughly and dry. Give it a rough chop.
Make the dressing - Stir together the mayo, preserved lemon, tarragon, and scallions. Season with salt and pepper to taste.
Combine and serve - Fold the shrimp and celery into the dressing. You can serve right away, but this salad is even better if you give the flavors some time to meld.