Step 1 Pour the seafood stock into the same saucepan used to fry the garlic. Add the lemon juice and sugar and bring the mixture to a boil over medium heat. Add the onions and tomatoes. Cover the pan, reduce the heat to low, and simmer for 5 minutes, or until the onions are translucent and the tomatoes are mushy.

Step 2 Put the fish in a strainer or colander and dunk it into the simmering broth. Cook for 3 to 5 minutes, until opaque throughout. Be careful not to overcook it. Immediately transfer the fish to a plate and set it aside.

Step 3 Put the beans in the strainer and dunk it into the simmering broth. Cook for about 5 minutes, or until the beans are tender but still vibrant green. Transfer the beans to a plate and set it aside.

Step 4 Put the chiles and water spinach in the strainer and dunk it into the simmering broth. Cook for about a minute, or until they are tender but still vibrant in color. Transfer the chiles and spinach to a plate and set it aside.

Step 5 While the broth continues to simmer, taste and add fish sauce and more lemon juice as needed. Distribute and arrange the fish, shellfish, and vegetables into each of four bowls.

Step 6 Remove the broth from the heat and ladle it into the bowls with the seafood and vegetables. Serve the soup piping hot, with rice or crusty bread.