Rinse the Garoupa fish head pieces under cold water and pat them dry.
In a blender or food processor, combine the dried red chili paste, peeled shallots, turmeric, and belacan. Blend until smooth, adding a little water if necessary to create a thick paste.
In a large pot or wok, heat the oil over medium heat. Once hot, add the spice paste and sauté for about 5-7 minutes until fragrant.
Gently add the chopped Garoupa fish head pieces to the pot, stirring them into the spice mixture. Cook for about 2-3 minutes.
Pour in 2.5 cups of water and add the tamarind pulp. Bring the mixture to a gentle boil, then reduce heat to a simmer. Cook for about 15 minutes.
Add the okra, lemongrass, and polyganum leaves to the pot. Stir well and let simmer for another 10 minutes.
Taste the curry and season with salt and optional sugar as needed. Adjust seasoning to your preference.
Once cooked through and the fish is tender, remove from heat. Garnish with sliced bunga kantan and mint leaves if desired.