Pat salmon fillets dry on both sides with a paper towel. Rub all over with oil, then season with salt and pepper to taste. Sprinkle 1 teaspoon of Cajun seasoning on top of the salmon fillets.

Heat a pan over medium-high heat, place salmon fillets, skin side-up (if using with skin), and sear the tops for about 4 to 6 minutes, flip the salmon, and cook an additional 6 to 8 minutes, until the salmon flakes separate easily. Turn off the heat. Salmon cooking times will vary by the thickness of the salmon pieces.

While the salmon cooks, combine the softened butter with the remaining 3 teaspoons of Cajun seasoning (1 tablespoon) in a small dish.

Place a generous dollop of Cajun butter on top of each salmon fillet, allow it to melt for 30 seconds and plate the salmon. Use the back of a spoon to spread Cajun butter over the top.