Place the mung beans in a pressure cooker, smaller the cooker, the better. Wash them thoroughly after checking for stones. Add two cups water to mung, close cooker, fit the whistle and keep the flame on medium-high.
After one whistle, reduce flame to minimum until 3-4 more whistles are let out. Remove cooker from flame and let cool.
While the beans are cooking, you can prepare the masala. In a kadai / wok, heat the oil. Splutter the cumin and mustard seeds, add a pinch of asafoetida with the flame on medium. Add the ginger, chillies, onions with a pinch of salt, saute for 5 minutes or so, until the onions are soft.
At this point, add the tomatoes with the spices (turmeric, garam masala, subzi masala) with the remaining salt. Stir it well for 3-4 minutes until the masala comes together as a rough paste.
Once the cooker has cooled off, release the pressure and open the lid. The mung beans must have cooked to a soft consistency and not entirely mushy. (If they are not cooked enough, then keep them back with some water for one more whistle on a medium flame) Empty the cooked mung beans into the masala. If very thick, add 1/2 cup water and boil the mung for 2 minutes along with the masalas.
Adjust salt as per taste and remove from flame. Garnish with coriander leaves. Serve hot with rice, rotis or bread, along with slices of lime and a bowl of yogurt.