Add oil to a wok and bring to 180°C. Shallow fry the fish, in two batches, for 3-4 minutes or until crisp and golden. Remove from oil and drain. Transfer the hot oil into an oil pot to cool, reserving 1 tablespoon in the wok.
To the wok, add the lemongrass, finger root, garlic, galangal and onion. Stir-fry for 2 minutes or until fragrant.
Return the fish to the wok. Add the green peppers, kaffir lime, red chillies, fish sauce, oyster sauce and sugar.
Stir-fry for a further 3 minutes. Squeeze with lime juice and transfer to a serving plate.
Garnish with Asian basil to serve.