Preheat oven to 350 degrees F.
Pat the fish dry with paper towels.
Place fillets on a parchment-lined baking sheet or a greased baking dish.
Brush the tops of the fillets with the oil.
Combine the salt, mustard, paprika, black pepper, and red pepper flakes in a bowl. Stir to mix.
Sprinkle the seasoning over the fish. Rub the seasoning into the fish gently with your fingers.
Bake for 15 to 20 minutes, until fish reaches an internal temperature of 145 degrees F on an instant-read thermometer and flakes apart easily with a fork.
