If using tamarind paste, dissolve 1/4 cup tamarind paste in 1 cup of warm water. Stir well and strain to remove any seeds and fibers. Set aside the tamarind juice.
In a large pot, bring 4-5 cups of water or fish stock to a boil.
Add the fish chunks and cook for about 5-7 minutes until the fish is nearly cooked through. If using shrimp or chicken, adjust the cooking time accordingly (shrimp will take about 3-4 minutes, chicken will take about 10-12 minutes).
Add the tomato wedges, pineapple chunks, okra, and taro stems to the pot.
Reduce the heat to a simmer and cook for an additional 5-7 minutes until the vegetables are tender but still vibrant.
Pour in the tamarind juice, starting with half and adding more to taste.
Add the fish sauce, sugar, and a pinch of salt. Stir well and taste the soup, adjusting the seasoning as needed.
If desired, add sliced fresh chili for a spicy kick.
Just before serving, add the chopped cilantro, rice paddy herb, Thai basil, and green onions to the pot.
Stir gently and allow the herbs to infuse the soup with their aroma for about 1-2 minutes.
Ladle the Canh Chua into serving bowls, making sure each bowl gets a good mix of fish, vegetables, and broth.
Serve hot, accompanied by steamed white rice. You can also provide extra fish sauce and sliced chili on the side for individual seasoning.