Heat a large cast iron skillet over medium-high heat and add the olive oil.
Pat the salmon filets dry with a paper towel and rub the cajun seasoning onto all sides of the salmon filets.
Place the filets top side down in the hot skillet and cook on the first side for about 5 minutes, or until the sides begin losing their shine and colour and a golden crust forms on the first side.
Flip the fillets and cook on the second side for about 5 more minutes, or until the filets reach an internal temperature of 145 degrees Fahrenheit (63 degrees Celsius) and are safe to eat.
If you're worried about over-browning, reduce the heat slightly and place a lid on the pan for about one minute. This will help the filets cook through.
Serve immediately alongside your favourite side dishes or over a salad.