1) Preheat oven to 180C/Gas 4.
2) Season salmon with seafood cajun seasoning. In a medium saute pan, saute salmon in butter on medium-high heat, fat side down, until golden brown. Using a metal spatula turn salmon over and cook until golden brown. Transfer salmon onto a sizzle plate or small sheet tray and place in oven for 4-6 minutes. Remove from oven and let rest.
3) Slice ciabatta roll lengthwise and place under grill until lightly golden. Spread goat cheese and lemon mayonnaise on roll. Arrange salmon, lettuce, tomatoes and onions on roll.
Seafood cajun seasoning:
In a medium bowl, combine cayenne pepper, salt, paprika, black pepper, garlic, onion powder, gumbo file and crab boil seasoning.
Goat cheese and lemon mayonnaise:
In a medium bowl, mix goat cheese, mayonnaise, lemon juice, parsley, salt and freshly ground black pepper, to taste.