Using a mortar and pestle or a food processor, pound or blitz the coriander root, garlic, chopped galangal, lemongrass and chillies into a paste.
Heat the oil in a wok set over a medium heat. Stir-fry the paste you have made for a few seconds until it is fragrant, then stir in the oyster sauce, soy sauce, sugar and black peppercorns.
Add the squid, prawns, mussels and scallops, tossing to combine.Season with the fish sauce, then add the lesser galangal, green peppercorns and onion and combine well.
Pour in the Chinese rice wine and a bit of water to loosen the sauce.Cook over a medium heat for a few minutes until everything is cooked through.Add sweet basil leaves and turn off heat. Serve hot with jasmine rice.