Pat the fish fillets thoroughly dry with paper towels to remove excess moisture.
In a small bowl, combine the melted butter, lemon juice, lemon zest, and ¼ teaspoon kosher salt. Stir until well combined and set aside.
In another small bowl, combine the remaining ¼ teaspoon salt with the paprika, garlic powder, onion powder, and black pepper.
Season the fish evenly on both sides with the spice mixture, gently pressing the seasoning onto the fillets.
Heat the olive oil in a large, heavy skillet over medium-high heat. Once the oil is hot, add two fish fillets, leaving enough space between them for even browning.
Cook for about 2–3 minutes on the first side. Flip carefully and cook for another 2–3 minutes, or until the fish is opaque, lightly browned, and flakes easily.
Drizzle a small amount of lemon butter sauce over the fish toward the end of cooking. Repeat with the remaining fillets, avoiding overcrowding the skillet.
Transfer the Lemon Butter Fish to serving plates and spoon the remaining sauce over the top.
Garnish with fresh basil or parsley and serve with lemon slices.