Slice the white part of the green onion thinly, soak in water for 5 minutes, then drain.

Cut the garlic chives into 3 cm pieces. Pat the mackerel fillets dry with paper towels.

Heat salad oil in a frying pan, place the mackerel skin-side down, season with salt and pepper, and cook until golden brown. Flip and cook through, then remove from the pan.

In the same pan, add soy sauce, sugar, vinegar, and water. Bring to a boil, then add garlic chives and cook for 30 seconds over medium heat.