Put the cornflour on a plate and dredge the fish fillets through it, patting them to make some of the cornflour stick.
Fry the fish until golden. This should take 3-4 minutes. Lift out and drain on kitchen paper.
Pour a little groundnut oil into a hot wok. When very hot add the garlic, chillies and spring onions . Stir quickly then add the soy, fish sauce, sugar and 2 tbsps water. Stir in the basil and coriander.
Put the fish on hot plates and pour over the sauce. Serve immediately.