Break the maitake mushrooms into smaller pieces by hand. Finely chop the green onion.

Drain the canned mackerel and roughly flake the fish.

In a pot, add water and dashi powder. Bring to a boil over medium heat, then add the mackerel and maitake mushrooms. Cover and simmer on low heat for 4-5 minutes.

Turn off the heat and dissolve the miso paste into the soup. Heat gently over medium heat until just before boiling.