Clean Lapu-Lapu well, then slice into fillets. Remove any sharp bones (you can use tweezers to do this).
In a large casserole, heat the corn oil to medium heat. Sauté the onions until tender. Stir in the garlic, then add the tomatoes. Sauté until the tomatoes are wilted. Add the miso paste and continue sautéing to blend the miso with the other ingredients.
Pour in the water and bring to a boil. When the water is boiling, add the eggplants, string beans, radish, and kamias. Lower heat to a simmer. Let simmer until the vegetables are almost tender, then add the Lapu-Lapu fillets, kangkong, and the long chilies.
When vegetables are tender, add the sinigang powder mix. Season with patis and continue simmering until the fish fillets are fully cooked (don’t overcook or the fish will disintegrate). Serve hot with rice and additional patis on the side. Makes three to four servings.