Ive tried making "Saba no Miso" or Mackerel with Miso
I changed the style a little bit for my own taste. But the 3 main ingredient is the one listed below.
Ingr. Mackerel, Miso, 1 teaspoon of vinegar, broth cube ( optional ), water
Mix water and vinegar and bring to boil ( the water will depend on your amount of fish , you can also increase the amount of vinegar )
Add Mackerel as soon as water starts boiling, boil for about 1 minute.
Mix miso and water and maybe broth cube ( i did not use broth cube )
Optional: I added a teaspoon of mirin and cooking wine.
Then put the boil mackerel and bring to boil in a medium heat for about a minute or 2. And then your done
Found this in a 5 min. cookbook , but as I said I change/add some more spicies