Fill a 2-quart saucepan with 3 cups of water, 2 teaspoons of the Creole seasoning, bay leaves, celery seed, garlic, and 1 tablespoon of the lemon juice, and bring to a boil over high heat. Add the shrimp, reduce the heat to medium-high, and cook for 4 minutes.
Drain the shrimp in a colander, add a couple handfuls of ice, and give the shrimp a few tosses to cool them down. Once cool enough to handle, remove the aromatics and place the shrimp between several layers of paper towels to dry. (You can dump the aromatics; they've done their job.) Roughly chop the shrimp and set aside.
Whisk the mayonnaise, mustard, remaining lemon juice, pickle relish, celery salt, black pepper, and remaining Creole seasoning together in a large bowl. Fold in the scallions, celery, chopped shrimp, dill, and tarragon.
Refrigerate for at least two hours, or better yet overnight, before serving in lettuce cups.