Pat the mackerel dry with paper towels, cut into two pieces, and score the skin. Heat salad oil in a pan and place the mackerel skin-side down. Cook over medium-low heat until browned, flip, and cook until fully done. Add the seasoning ingredients and bring to a boil. Cover and simmer on low heat for 3 minutes.

Boil water in a pot and cook the somen noodles according to package instructions. Rinse under cold water and drain.

Add the cooked somen noodles to the pan with the mackerel and simmer briefly until warmed through.