Heat the oven to 475°F with a rack in the middle position.
Whisk together the miso and honey in a small bowl. Lay the fish fillets in a 6 by 10-inch glass baking dish and brush with the glaze.
Bake until the fish reaches an internal temperature of 135°F, 15 to 20 minutes. Remove from the oven and let rest in the dish for 5 minutes before serving.