Season the mackerel fillets on both sides with salt and pepper and add the fish to the pan, skin-side down (you may need to do this in batches). Fry for 3 minutes, without moving the fillets ...

Score the kahawai skin in a criss-cross pattern. Dredge the fillets in tapioca flour. Heat shallot oil in a pan and fry the fillets, skin side down on medium heat. Flip over and cook until done.