1. Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper or lightly grease it to prevent sticking.
2. Pat the salmon fillets dry with paper towels. This step is crucial for getting a nice crust when baking.
3. In a small bowl, combine the Cajun seasoning, smoked paprika, garlic powder, onion powder, cayenne pepper (if using), salt, and black pepper.
4. Brush each salmon fillet with olive oil on all sides. This helps the seasoning stick and keeps the fish moist during baking.
5. Sprinkle the spice mixture evenly over the salmon, pressing gently to adhere.
6. Place the fillets on the prepared baking sheet, skin-side down if the skin is on.
7. Bake for 12-15 minutes, depending on the thickness of your fillets. The salmon should flake easily with a fork but still be moist inside.
8. Remove from the oven and let rest for a couple of minutes. Garnish with lemon slices and chopped parsley before serving.

Here’s a little secret I picked up from my grandma: resting the salmon after baking lets the juices redistribute, making each bite tender and flavorful. And if you like a bit of crisp on your fish, you can broil it for the last 2 minutes, but watch closely to avoid burning.