First, take your salmon fillets out and pat them completely dry with a paper towel. This step is crucial because removing excess moisture helps the skin get crispy and allows the surface to sear nicely. Once dry, brush each fillet on all sides with olive oil.
Now it's time for the flavor. Sprinkle the Cajun seasoning, salt, and pepper evenly over both sides of the salmon fillets. Don't be shy with the seasoning; you want a nice, flavorful crust to form when it hits the heat of the grill.
If you have some extra time, I highly recommend the marinade. In a small bowl, whisk together the Dijon mustard, honey, fresh lemon juice, and minced garlic. Coat the salmon fillets in this mixture and let them marinate in the refrigerator for at least 30 minutes.
Preheat your grill to a medium-high heat, around 400-450°F. If you're using a charcoal grill, wait until the coals are covered in a light gray ash. For a gas grill, simply close the lid and let it heat up for about 10-15 minutes. Clean the grates and oil them well to prevent the salmon from sticking.
Place the salmon fillets on the hot grill, skin-side down. The skin will protect the delicate flesh from the direct heat. Close the lid and let them cook for about 6 to 8 minutes. You'll see the color change from the bottom up as it cooks.
Using a wide spatula, carefully flip the salmon fillets. Cook for another 4 to 6 minutes on the other side. The salmon is done when it flakes easily with a fork or when an instant-read thermometer inserted into the thickest part reads 145°F.