Rinse the fish steaks under cold, running water and drain thoroughly in a colander. Cut the steaks into six pieces and place in a bowl.
Add the Miso Marinade to the fish steaks and toss lightly to coat the fish steaks. Cover with plastic wrap, and refrigerate. Let marinate for at least 1 hour, or for several hours.
Prepare a medium-hot fire for grilling and place the grill about 3 inches above the coals. Remove the fish from the Miso Marinade, spreading the Marinade with your hands so that there is a light coating. Arrange the fish steaks on the grill and cook about 5 to 6 minutes on each side, or until the flesh is opaque all the way through. Alternatively you may broil the fish about 7-9 minutes on each side, or until the fish flakes when prodded with a knife. The miso glaze should bubble and brown at the edges. Remove and serve with steamed rice and stir-fried or steamed vegetables.