Pat the catfish fillets dry with paper towels.
In a small bowl, combine all the dry spices: paprika, oregano, thyme, cayenne, garlic powder, onion powder, black pepper, and salt.
Brush both sides of each fillet with melted butter, then generously coat with the spice mixture, pressing gently to adhere.
Heat a large cast-iron skillet over medium-high heat until it's very hot (about 5 minutes).
Add olive oil to the heated skillet.
Place the seasoned fillets in the hot skillet (don't overcrowd) and cook for 3-4 minutes on each side, or until the fish flakes easily with a fork.
Transfer to serving plates and squeeze fresh lemon juice over the top.