Place all curry paste ingredients (garlic, ginger, chillies, coriander stalks, onion, turmeric, cumin, water) into a food processor and blitz until smooth
Place a wok or pan over medium heat and add the mustard seeds
Toast mustard seeds until they pop then add ghee or butter
Add the curry paste and turn up the heat, frying for 1-2 minutes while stirring continuously
Add coconut milk and 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
Transfer to a dish and drizzle with chilli oil
Top with fresh herbs and fried shallots
