Heat a large, heavy-bottomed pot over medium-high heat, then add a tablespoon of oil.
Lightly season the pork belly pieces with salt. Sear them until lightly browned on both sides, being careful of the splatter.Once browned, transfer the pork to a plate. Then, carefully remove any excess fat or oil from the pot.PRO TIP: Searing the meat for Sinigang, though not traditional, creates a rich caramelization, giving the soup a deeper, more complex flavor. Reduce the heat to medium and saute garlic, onions, and tomatoes until the softened and caramelized, stirring occasionally. This step will infuse the base of your dish with rich, aromatic flavors.
Add the pork and the sinigang mix, then pour in about 7 cups of water. Turn up the heat and bring the mixture to a boil. You can always add more water later if needed to adjust the consistency or taste of the broth.
Cover the pot and reduce the heat to medium-low. Let it simmer for about 30 minutes or until the pork becomes tender. As the soup simmers, you may notice foam and fat rising to the surface. Skim this off with a spoon for a clearer broth. Add the radish and taro root, then cover and simmer for another 10 minutes until the vegetables are tender.
Add the chili peppers, eggplant, and okra. Cook for another 5 minutes until the vegetables are tender.
Season with fish sauce, salt, and pepper to taste. Add the bok choy and yardlong beans, then cover and turn off the heat. Let them cook in the hot broth for about 2 minutes.