Peel and grate the ginger. Chop the green onions into small rings.
If you have a whole mackerel, fillet it. If you have a fillet with bones, try to cut or use a pair or tweezers to remove the bones. Cut into pieces small enough to pound.
Pound the mackerel on a cutting board. Once it's come together, add the miso and spices, pound well, mix, and it's complete! Chill well before serving.
Story Behind this Recipe
My father sometimes made this namero. I couldn't get enough of the flavor. It's really delicious eaten with hot rice. I recommended this to my friends who like drinking (primarily shochu and sake) and they fell in love with it. Even now apparently when they go out drinking they look for namero.
You can add other spices such as myoga ginger. I don't have any specific recommendations for the miso. Use whatever's at home. If the miso you have tastes very strong, you might want to add less. You could enjoy this as an ochazuke, as a rice porridge if you find the flavors are a bit too pronounced.