Thinly slice the onion, red bell pepper, and celery. Set aside.

Pat the mackerel dry and coat it evenly with potato starch.

Heat vegetable oil in a pan over medium heat and pan-fry the mackerel until golden brown on both sides. Remove and set aside.

In a small saucepan, combine all ☆ Nanban Vinegar Sauce ingredients and bring to a gentle boil. Stir until sugar dissolves, then remove from heat.

In a large bowl, combine the fried mackerel, sliced vegetables, and the Nanban Vinegar Sauce. Mix gently to coat everything evenly.