Prepare the mackerel by removing large bones, soaking it in rice water for 20–30 minutes to remove the fishy smell, rinsing it under cold water, and cutting it into 2–3 pieces with slits.

Place the mackerel on a kitchen towel to drain excess water.

Slice the onion, green onion, and chilies.

Mix all the teriyaki sauce ingredients in a small bowl.

Place the mackerel in a plastic bag, add 2 tbsp of cornstarch, and shake to coat the fish evenly.

Heat a pan with a small amount of cooking oil and fry the mackerel skin-side down first.

Flip the mackerel and lightly fry the other side.

Pour the prepared teriyaki sauce into the pan and bring it to a boil.

Add the onion and fried mackerel to the pan, spooning the sauce over them.

Add the green onion, green chili, and red chili, and continue spooning the sauce over while simmering.