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.
Melt the butter in a small bowl. Brush the melted butter over the flesh side of the salmon fillets, then sprinkle the spice mixture evenly over the flesh and lightly pat to adhere as needed.
Heat a large cast iron skillet or other heavy-bottomed pan over medium heat (no oil). Turn on the exhaust fan and open a window if things start to get smoky. When the pan is very 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, then carefully turn each piece 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 on fillet thickness; 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, transfer the fillets to serving plates, and sprinkle with chopped fresh parsley or thyme; serve with additional lemon wedges.