Heat a 12-inch (seasoned) cast-iron skillet over very high heat to the smoking stage.
Meanwhile, dip each fillet in the melted butter in order to coat both sides. Sprinkle Tony Chachere's Spice -n- Herb Seasoning generously on both sides of the fillets. Place fillets in the hot skillet. Pour 1 teaspoon of butter on top of each. Cook, uncovered, until the underside looks lightly charred (about 2 minutes). Turn the fish over and pour 1 teaspoon butter on top. Cook until fish is cooked through. Repeat with remaining fillets. Serve piping hot.