Pat fish dry with paper towels. Sprinkle both sides with Cajun seasoning and salt.
Heat a large skillet and add olive oil to skillet. Add the seasoned fish, and let cook, undisturbed until the bottom is blackened, about 1 to 3 minutes, depending on the thickness of the fish.
Carefully flip the fish over and continue cooking until the fish lightly flakes, about 1 to 3 minutes depending on the thickness of the fish.