Preheat the oven to 350 F/180 C/Gas Mark 4.
Lightly butter a shallow baking dish that is large enough to hold the fish fillets in a single layer.
Pat the fish fillets with paper towels to dry.
Arrange the redfish fillets in the prepared baking dish skin-side down (if there is skin on the fillets).
Redfish fillets placed in a single layer in the greased baking dish
In a cup or small bowl, combine the 1/4 cup of melted butter with the lemon juice, onion, paprika, salt, and pepper.
Melted butter combined with lemon juice, chopped onion, and spices in a bowl
Pour the butter and seasoning mixture over the redfish fillets.
Pouring the seasoned butter over the redfish fillets in the baking dish
Bake in the preheated oven for about 20 minutes, or until it reaches an internal temperature of at least 145 F/63 C. The fish should flake easily with a fork when done.
Flaking the baked redfish fillets with a fork
Serve the redfish with lemon wedges and rémoulade sauce, if desired.