To make Remoulade sauce, mix all ingredients together, cover and refrigerate until ready to use.
Thoroughly rinse shrimp and drain any excess water.
In a bowl stir together buttermilk and tablespoon of seasoning, either Cajun or Old Bay, add shrimp, cover, and marinate for at least 30 minutes.
In a pie plate or shallow bowl stir together flour, salt, pepper, garlic powder, and paprika until thoroughly combined.
Prepare two cookie sheets with cooling racks on top of each.
In a large Dutch oven or cast-iron pan, add 1-2 quarts of vegetable oil, oil needs to be at least 1 ½ inches deep. Using a kitchen thermometer, heat oil to 375 degrees on medium high heat.
While oil is heating, coat shrimp. Drain off buttermilk and coat in seasoned flour and place coated shrimp on one of the prepared cookie sheets. Having all shrimp breaded before frying begins makes for an easier workflow.
When oil is heated, fry shrimp in batches of 6-8 for 2 minutes, or until fully cooked. Carefully remove shrimp with a slotted spoon and place fried shrimp on the second prepared cookie sheet to drain any excess oil.
To assemble sandwich, cut open bread and spread with 1-2 tablespoons of Remoulade sauce, top with lettuce, tomato, pickle and 4-5 shrimps.