Heat oil in a pan and add the items to temper. Fry them until mustard seeds cracks, and urad dal turns brown. Add small onions and garlic now. Saute them well for 5 minutes or until they turn brown. Add tomatoes and fry them until soft and mushy.
Once the tomatoes are cooked well add tamarind water, red chili powder, coriander powder, sambar powder, and salt. Mix it well and boil the kuzhambu for 5 minutes until the raw smell of tamarind completely leaves.
Once the raw smell of tamarind leaves, add pressure cooked agathi keerai and mix it with the boiling kuzhambu. Boil the kuzhambu again for five more minutes in medium flame.
Then add the ground spice powder to the kuzhambu and mix slowly after without forming any lumps. Add water if needed. Boil the kuzhambu again for five more minutes in medium-low flame. Once the kuzhambu becomes thick, switch off the flame.