Bring about 2 liters of water to a boil in a medium saucepan.
Pour another 2 liters of water into a separate pot and bring to a boil (for flash steaming the seafood).
While waiting for the water to boil, chop up the galangal, lemongrass, tomato, cilantro, scallops, shrimp, squid, snapper and mussels.
Once the water in the first pot comes to boil, add the lime leaves, mushrooms, chiles, galangal and lemongrass and stir. Immediately after, add the fish sauce, lime juice, prik pao and sugar. Let the broth simmer.
Flash-steam the seafood in the other pot for approximately 1 minute. Add the seafood to the main pot, stir and boil for about 5 minutes.
Ladle the soup into bowls and top with some tomato and cilantro.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.