Cook moong dal with turmeric powder in the pressure cooker. Soak tamarind in warm water for 15 minutes and extract juice or alternatively dissolve tamarind paste in a cup of warm water. Chop green chillies into halves or quarter and tomatoes into 8 pieces.
Heat oil in a pot and add mustard.
As it splutters, add methi seeds, asafoetida and curry leaves.
As methi seeds turn golden, add tomatoes, chillies and sambar powder.
Saute for a min and add tamarind juice and salt.
Let it boil for 5 minutes.
Add water in the middle if required.
Add cooked moong dal and jaggery to this.
Let it boil for another 5 minutes.
If you prefer a thicker sambar, dissolve rice flour in water and add it to the sambar and let it boil for another 5 minutes.