Prepare the brine by mixing buttermilk, cornstarch, salt, lemon juice and spices.
Ensure the catfish is submerged and allow to brine for at least 4 or up to 24 hours.
Prepare a pan on medium heat with at least 1 inch of neutral oil. Prepare breading by mixing pecan flour and gluten free breadcrumbs.
Pull the catfish fillets out of the brine and lay over the breading mix. Scoop the mixture over the top and press firmly to ensure it sticks to the fillet.
Pan fry the catfish using a spatula to flip after 1-2 minutes. Total cooking time should be around 4-5 minutes.
Prepare the remoulade by placing all ingredients in a blender or food processor. Blend until fully incorporated and only small pieces of parsley are still visible.
Prepare the sandwich by liberally spreading (about 2 Tbsp) remoulade on each side of the bread. Lay a bed of lettuce on the bottom, followed by catfish, tomatoes and pickles. Serve immediately.
