In a large pot, bring the water to a boil. Add the pork chunks and cook for 5-7 minutes to remove any impurities. Drain and rinse the pork.
Return the pork to the pot with fresh water. Bring to a boil again and then reduce to a simmer. Cook for 45 minutes to 1 hour, or until the pork is tender.
Add the quartered onion and tomatoes to the pot. Continue to simmer for another 10-15 minutes.
Stir in the tamarind paste or tamarind soup base mix. Adjust the amount based on your preferred level of sourness.
Add the radish, green beans, and eggplant. Cook for an additional 5-7 minutes, or until the vegetables are tender.
Stir in the chopped kangkong or spinach and cook for another 2-3 minutes until the greens are wilted.
Season the soup with fish sauce, salt, and black pepper to taste. Add the green chili peppers if you like a bit of heat.
Enjoy your meal!