Thaw shrimp if frozen, remove tails and cut shrimp into quarters and place in bowl with scallions and celery. Chill in refrigerator for about 1 hour.
Whisk together all sauce ingredients, then salt and pepper to taste. Keep in refrigerator for one hour to allow flavors to blend.
Add shrimp, scallions and celery to sauce, mix well and distribute equally into 4 chilled cocktail glasses. Garnish with cilantro leaf and serve.