Clean and fillet the fish, then remove the bones from the fillets (tweezers are useful for this). Cut each fillet into 3 pieces.
Coat both sides with mayonnaise (it's easier to put the fish in a bowl to do this; be careful not to break them, though). Coat with panko.
Heat oil in a frying pan, and fry both sides to a crisp.
The mayonnaise has a lot of flavor so these are delicious as-is, but if you like, serve with ponzu or sauce.
Story Behind this Recipe
Horse mackerel prepared in salt can be a little bland, so my partner doesn't really care for it. My partner and children eat a lot more when it's breaded. Fried foods can be a bit of a hassle so I substituted tasty mayonnaise for the usual flour + egg for a breaded version.