Mix the spices, salt, and pepper with a small whisk or fork in a bowl to create the blackened seasoning mix. Set it aside.
Pat dry the salmon fillets and arrange them, skin side down (if using salmon with the skin on), in a dish or tray. This will serve as your station for coating them with the blackened seasoning.
Brush melted butter over the salmon fillets, then immediately sprinkle a tablespoon of the seasoning over each piece to ensure it’s fully covered. If you use skinless salmon, reserve some of the seasoning for later (to sprinkle on the other side while cooking).
Place a piece of parchment paper over the seasoned salmon, pressing down firmly to help the seasoning adhere to the butter. This tip helps prevent messy hands, especially when hurrying to cook the salmon on a weeknight.
Turn on your vent or fan above the stove, then heat a nonstick pan or skillet with the vent or fan on medium-high heat. Once the pan is hot, carefully place the salmon fillets seasoned side down onto the skillet and let them cook undisturbed for about 6 minutes. If you think the heat is too high, reduce it slightly. However, the pan must be hot to achieve that signature charred, blackened texture.
Brush some melted butter over the top side and sprinkle the remaining seasoning if using skinless salmon. There’s no need to press down; just let it sit on top and mesh with the butter.
Using two spatulas, slide one underneath a salmon piece and use the other to hold it in place as you gently flip it over. It should be sizzling, charred and nicely blackened, or dark brown.
Cook for about six more minutes until the sides change to a light pink and meet in the middle. For the salmon to be fully cooked, a temperature reading should be between 135°F and 145°F. Let it rest for a few minutes before serving.
Add lemon wedges, fresh arugula, and baby tomatoes around the salmon before serving.