Heat the oven to 475 degrees F.
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. Put the dish in the oven on the middle rack and bake until the fish reaches an internal temperature of 135 degrees F on an instant-read thermometer, about 15 to 20 minutes. Remove from the oven and let rest in the dish for 5 minutes before serving.