Cut the fish into strips, season with salt and pepper and turn in the cornstarch. Fry all over over high heat, drain on kitchen paper.
Heat 2 tablespoons of the frying oil in a wok or pan and stir-fry the shallots, lemongrass, chilli, ginger and shrimp paste for 3 minutes. Add the water, soy sauce, ketjap manis and sugar and let it boil down a little. Add the lime juice, spring onions and fish strips.