Preheat oven to 375 degrees. Rack should be on the middle or upper third of the oven.
If the skin is on the ling cod, score the skin side with a few slashes with a paring knife about 1/2" deep. This will allow the glaze to penetrate through the skin and keep the fish from curling when cooked.
Mix together glaze ingredients. Rub onto fish and let marinate for 15 minutes.
Place fish fillet on a baking sheet, lined with foil or not, and rubbed with a bit of oil or non-stick spray. Roast fish for 10-15 minutes until fish is cooked through or 145 degrees . Time will depend on the thickness of the fillet.
Notes
If you have a skin-on fillet, score it with a few slashes, so the fillet won't curl while cooking.
Use whichever color miso you have on hand - red, white or yellow will do.
Marinate with the glaze from 15 minutes to overnight.
Check for doneness when you can easily pierce through the thickest part of the fillet with a fork or a thermometer reads 145 degrees.
If the fish starts to ooze white cream, it is turning well done and should be removed from the oven immediately.
To remove fish odors from your oven, bake lemon or orange peels in the oven at 325 degrees until you start to smell citrus freshness.