Mince the onion and place it in a microwave-safe container. Cover loosely with plastic wrap and microwave at 600W for 2 minutes. Let cool. Mince the ginger.

Remove bones from the horse mackerel fillets and finely chop them. Use a knife to mince until they resemble ground meat.

In a bowl, combine the minced onion, horse mackerel, ginger, and the ☆ ingredients. Mix until sticky and well combined. Divide into two portions and shape into oval patties with a slight indentation in the center.

Heat salad oil in a frying pan over medium heat. Add the patties and cook until browned. Flip, cover with a lid, and cook on low heat for about 5 minutes until cooked through. Transfer to a plate.