1) Make the sweet potato chips: preheat an oven to 180°C.
2) Put the olive oil, sea salt, crushed dried chilli flakes and black pepper into a roasting tin. Add the sweet potato slices and turn them to coat in the seasoned oil. Roast in the oven for 20 to 30 minutes, depending on the thickness of the chips.
3) For the goujon marinade: in a shallow dish, mix together the onion, rice wine, and ginger. Add the fish and, marinate for 20 minutes, covered, in the refrigerator.
2) For the sauce: in a small pan, heat the lemon juice, hoisin sauce, soy sauce, and chile flakes and thicken the mixture with the cornstarch and water slurry, if necessary. Set aside.
Cook's Note: If your sauce is a little sharp, add a pinch of caster sugar.
3) For the bread crumbs: mix the crushed chillies, salt, white pepper together in a bowl. Add in the bread crumbs, then tip them onto a plate or tray. Set aside.
4) For the coating: remove the fish from the marinade and dip the strips in the flour, shaking off the excess flour, then in the eggs and, finally, in the seasoned bread crumb mixture.
5) Heat a wok over high heat and fill it to a quarter of its depth with enough groundnut oil. Cook's Note: Ensure your wok is stable before you deep-fry.
6) Heat the oil to 180°C. Test the temperature by dropping a cube of bread into the oil and seeing if it in turns golden brown within 15 seconds. Deep fry the coated fillets until they are golden brown. Remove them with a slotted spoon and drain them on an absorbent paper towel. Serve immediately with the sauce and roasted sweet potato chilli chips.