Put dahl in about 3 cups water and let boil. It normally takes about an hour for the dahl to break up and pulp, howe'ver what I do is to start soaking it in water before I leave for work. This way it takes much less time to cook when boiled later. (gas, electricity SAVINGS!!)
Spice Mixture: (To be added when dahl is about 80% cooked or even earlier if you like) Slice the onion into thin slices. Heat the oil in a frying pan, when hot, add red chilies and mustard seeds. After seeds pop, add the asafoetida, and immediately turn down the heat. Add the onions, start frying on low heat until they are transparent, then turn up heat until they are quite brown, but not burnt black. Add coriander & turmeric and turn down heat. After a minute, add about 0.5 cup of the boiling dahl mixture to the frying pan and stir energetically so that the spice mixture gets mixed well, and onions break up.
Pour it back into the dahl pot, add salt, cook for another 10 minutes or until dahl is done, whichever comes later.