Place the prepared mustard into one bowl, and add the cornmeal, salt and seasoning mixture in a separate bowl. Dip each fillet in the mustard, covering both sides. Then drop the fillet into the cornmeal mixture, and coat on both sides. In a large skillet, heat peanut oil until hot but not smoking, Carefully place one fillet into the skillet at a time. The fillet should sizzle immediately after being lowered into the oil. Place additional fillets into the pan, up to 3 fillets depending on size. Cook about 3 minutes or until brown, and then flip with spatula. Fry the second side about 2 minutes or until golden brown. Remove from oil and place onto a paper towel-lined plate. Repeat until all of the fillets are fried. Allow the fish to cool for about 5 minutes and serve.