Brush the fish filets with no-stick grilling marinade and let sit for one hour. Sprinkle the filets with the creole seasoning and grill over direct high heat until the center of the fish is slightly pink, about 6-8 minutes. Turn the filets once during cooking. Do not overcook.
Brush the inside surfaces of the hamburger buns with the olive oil. Grill over medium direct heat for 2-3 minutes.
To assemble the sandwiches, spread a small amount of the seafood remoulade on the toasted surfaces of the hamburger bun. Place onions on the bottom bun, enough to cover the surface, then top with the fish, tomato, lettuce and the top half of the bun.
Place onion and celery into a mixing bowl. Add remaining ingredients and blend well. Remoulade sauce tastes better if made at least 1 day in advance.
No-Stick Grilling Marinade
Place the egg yolks, Dijon mustard, and vinegar in a food processor. Blend on medium speed for 1–2 minutes.
Slowly drizzle oil into the mixture, 1 Tbsp at a time. If the marinade becomes too thick, add 1-2 Tbsp of warm water.
Once all of the oil has been incorporated, add seasoned salt, onion powder, paprika, cayenne pepper, garlic powder white pepper, black pepper, dry mustard, oregano, and thyme, until incorporated.