Finely chop the tomatoes and add to a saucepan with 2 cups of water
Bring to a boil until tomatoes are soft. Optional step: for a smoother consistency, blend the softened tomatoes with a hand-blender or food processor. Add back to the pot.
Add the salt, rasam powder, turmeric, and asafoetida.
Cook on a low flame for roughly 4 to 5 minutes, until it begins to bubble up
Mash the cooked dal and mix into the rasam.
Add approximately 1 1/2 to 2 cups of water, until you have a watery and thin consistency.
Cook on a low flame. When the rasam begins to froth, turn off the flame. Make sure the rasam does not boil.
Add lemon juice and stir.