Cut onion (shallots and onion) , tomatoes into small pieces. Cut drum stick to about 2 inches pieces. Cut egg plant into 4 vertical pieces or as you needs.
In a pressure cooker add onions, tomatoes, turmeric powder, asafoetida , thuvaram paruppu (Pigeon Pea / Red Gram) add 2 1/2 cup of water and pressure cook them for 4-5 whistle (note the Paruppu has to well done)
Now mash well the cooked paruppu, add 1/2 cup of water to it. add the cut drum stick, brinjal and pressure cook for another 1 whistle.
Now add the sambar powder, coriander leaves and salt to taste, mix well and cook for 5-10 min.
In another pan heat the oil add mustard seeds, fenugreek seeds(venthayam) , dry chili , cumin seeds(jeeragam) , curry leaves cook until the mustard seeds stop to splatter.
Now add this to the cooked sambar (pressure cooker). Mix well and serve.
Don't open pressure cooker when the pressure is still there.
Instead of pressure cooker you can use and pan to cook it, you have to be bit careful when the thuvaram Paruppu (Pigeon Pea / Red Gram) is cooked as it can burn really fast.