Heat the vegetable oil in a deep frying pan or wok over medium-high heat.
Carefully add the plathu fish to the hot oil and fry until golden and crispy on both sides. Remove the fish from the oil and set aside on a paper towel to drain excess oil.
In a separate pot, bring the water to a boil. Stir in the tamarind paste, palm sugar, fish sauce, sliced red chilies, and shrimp paste. Allow the mixture to simmer for about 5 minutes.
Add the cherry tomatoes, pineapple chunks, sliced long beans, and kaffir lime leaves to the pot. Let it simmer for another 10 minutes until the vegetables are cooked but still slightly crunchy.
Gently place the fried plathu fish into the pot with the other ingredients and simmer for an additional 2-3 minutes to allow the fish to absorb the flavors.
Remove from heat and garnish with fresh cilantro leaves.
Serve hot with steamed rice or as a soup on its own.
