Cut shungiku into bite-sized pieces and thinly slice the onion.

Drain the mackerel can and flake the fish.

Heat olive oil in a pan over medium heat, add the onion, and sauté until softened. Add the mackerel and continue to sauté.

Add water, milk, and a pinch of salt to the pan. Bring to a boil, then add the spaghetti, breaking it in half as you add it. Stir to prevent sticking. Cover and cook on low heat for the time indicated on the pasta package, stirring occasionally.