To make the curry paste, place all the ingredients into a food processor and blitz until smooth.
To make the curry, place a wok or pan over medium heat and add the mustard seeds. Toast until they pop then add ghee (or butter). Add the curry paste and turn up the heat frying off for 1 - 2 minutes, stirring continuously.
Add coconut milk, stir well, put the lid on and simmer for 5 minutes.
Add the fish cubes and poach on medium heat for 3 - 4 minutes, until just cooked through.
Season with light soy sauce, lime juice and sugar. Balance seasoning as desired.
To serve, transfer to a dish and drizzle with chilli oil. Top with fresh herbs and fried shallots.
