Season the fish chunks with salt and pepper and let stand in a cool place.
Put the fish head in a pot with 1.7L water and bring to a gentle boil over medium heat. Reduce the heat to medium-low and simmer until the liquid is reduced by 240ml, about 30 minutes. At this time you may discard the fish head if you wish.
Add the tamarind pulp, pineapple, tomato, and chilies and simmer for five minutes.
Add the fish chunks, adjust the seasoning, and simmer until the fish is cooked, three to five minutes.
Serve hot-in a communal bowl or individual soup bowls-garnished with holy basil, saw leaves (or coriander), and fried garlic oil as desired.