Clean the lapu-lapu by removing the gills and internal organs. Wash in running water and slice into 1 to 2 inches wide.
In a large pot pour 6 to 8 cups water and bring to a boil then add onions, tomatoes and tamarind juice (or sinigang mix) and simmer for at least 3 to 5 minutes.
Then add the fish and let it simmer again for another 8 to 10 minutes or until the fish is already cooked.
Season with salt or patis. You can add some magic sarap, namnam or any other granulated seasonings in the market.
Then add the all the vegetables and green chili then cook for 2 to 3 minutes.
Serve hot with fish sauce, kalamansi and red chili for dipping.