In a large pot, heat the cooking oil over medium heat. Add the chicken thighs, skin side down, and cook until golden brown. Flip the chicken and cook the other side until browned as well. Remove the chicken from the pot and set aside.

In the same pot, sauté the onions and tomatoes until softened and fragrant, about 3-4 minutes.

Pour in the water and bring it to a boil. Once boiling, reduce the heat to a simmer.

Add the tamarind soup base or tamarind concentrate to the pot. Stir well to dissolve it into the water, creating a flavorful sour broth.

Return the browned chicken thighs to the pot. Allow them to simmer in the broth for about 15-20 minutes or until the chicken is tender and cooked through.

Add the sliced daikon radish and eggplant to the pot. Simmer for another 5-7 minutes until the vegetables are tender yet still slightly crisp.

Season the sinigang soup with fish sauce (patis), salt, and pepper according to your preference. Adjust the sourness by adding more tamarind soup base if needed.

Once the vegetables are cooked, add the spinach or kangkong leaves to the pot. Let them wilt in the hot broth for a couple of minutes.

Remove the pot from the heat. Ladle the hot Chicken Sinigang soup into bowls. Garnish with sliced green chili peppers for an extra kick if desired.

Serve your Chicken Sinigang hot alongside steamed rice for a comforting and satisfying meal.