Wash the Urad dal thoroughly for 4-5 times or until the water runs clear. Soak it in enough water for 10-30 mins or more.
Simultaneously in a pressure cooker or vessel heat oil and add the cumin seeds.
Once they splutter add the asafoetida, green chillies, garlic and ginger (I use a food processor to get the fine consistency).
Cook for a min and then add the onions. Saute and cook until translucent.
Stir in the tomatoes along with salt, black pepper, chilli powder and coriander powder and turmeric powder. Mix well and cook till tomatoes are soft.
By this time usually the Urad dal must have swollen a bit. Drain the water from the dal and add it to this masala. Mix and cook till any water present in the dal almost dries out (approx 2 mins).
Then add 1 cup of water. Scrape the sides of the cooker if there is any masala stuck to it. Mix well. Close the pressure cooker lid and cook for 2-3 whistles ( I cooked mine for 2 whistles). Switch off and wait for the steam to escape completely.
Open the lid of the pressure cooker and fluff it up using a fork (don't over mix it or else you will break the dal). At this point there still might be some water left in the dal.
Add the garam masala, lemon juice and finely chopped coriander leaves.
Switch the gas on back to low heat and let this dal cook on low heat till the water (if any) completely dries out (approximately 5-10 minutes). Keep it open without any lid as this will help to dry out the liquid quicker.
Garnish with some more coriander leaves before serving. Dont over cook it too as the dal will get mushy.