Freeze horse mackerel fillets in a freezer bag for 45 minutes and store in the freezer.

Cut bell peppers in half, remove stems and seeds, and slice into six vertical pieces.

Defrost frozen horse mackerel in the refrigerator, sprinkle with salt, and coat lightly with potato starch.

Heat salad oil in a pan over medium heat, add bell peppers, and cook until browned. Remove from the pan.

Place horse mackerel skin-side down in the same pan, cook over medium heat until browned, then add seasoning mixture and simmer until glossy.