Place the salmon on a large plate, flesh-side up, and pat dry.
In a small bowl, stir together the paprika, brown sugar, salt, onion powder, garlic powder, cayenne, thyme and oregano.
In a separate small bowl, melt the butter. Brush the butter over the flesh-side of the salmon fillets, then sprinkle the flesh sides evenly with the spice mixture. Lightly pat the spices to adhere as needed.
Heat a large cast iron skillet or similar heavy-bottomed pan over medium heat (no need to add oil). Turn on the exhaust fan and open a window if things start to get smoky. Once the pan is completely hot (a droplet of water should dance on its surface), working quickly but gently, add the salmon fillets, one at a time, flesh-side down. Cook for 2 to 3 minutes without disturbing the fillets, until the surface is blackened (peek as little as possible so that the salmon gets a nice dark color), then carefully turn each piece of salmon over.
Continue cooking over medium heat, until the skin becomes crispy, and the fish is fully cooked through, about 5 to 6 additional minutes depending upon the thickness of your fillets. The fish should reach 145 degrees F on an instant read thermometer and flake easily with a fork at its thickest part.
Squeeze lemon over the salmon, then transfer the fillets to serving plates. Serve immediately with a sprinkle of fresh thyme and additional lemon wedges.
TO STORE: This salmon is best the day it is made, but you can store leftovers in the refrigerator for up to 1 day.
TO REHEAT: To avoid drying out your salmon, gently reheat it in a skillet on the stovetop over medium-low heat until just warmed through.