Heat the cooking oil in a thick pan or pot.
Saute the shallots, garlic and tomatoes just until softened.
Add the chicken and pour in the fish sauce.
Cook, stirring often, until the chicken has lost its raw appearance and the liquids have almost dried up.
Pour in water (or chicken broth), four to six cups, making sure that the chicken pieces are submerged in liquid.
Bring to the boil, lower the heat, cover and simmer until the chicken is tender.
Taste the broth and add more fish sauce, if needed.
Take the yard-long beans and radish and stir into the soup. Cover and simmer for about five minutes.
Taste the broth and add more fish sauce, as needed.
Add the kangkong stalks (the leaves go in last), stir and simmer for another five minutes.
Taste the broth, add more fish sauce if needed, then stir in the eggplants. Cover and simmer for five to seven minutes.
Check the broth again if more fish sauce is needed before stirring in the kangkong leaves. Simmer for another five minutes.
Pour in the tamarind extract, stir well and bring the soup to a simmer.
Give the broth a final taste, add fish sauce to balance the sourness of the tamarind broth, if needed, before serving your chicken sinigang.