Pressure cook the pigeon peas/toor dal with enough water and a pinch of turmeric powder. Mash and keep aside.
Soak the tamarind in 2 cup water and extract the pulp.
In a pan, heat 1 tsp oil. Add the ingredients for the masala except tomatoes and roast. Cool and add tomatoes and grind to a paste adding little water.
In the same pan, add 1 tsp oil and fry the radish for 5 minutes till the raw smell goes. Keep aside. Then fry the onion and capsicum for 2 minutes and keep aside.
In a vessel add the tamarind water and bring it to a boil. Once boil comes, add the radish and cook in the tamarind water.
When radish is 3/4th cooked, add the capsicum, onion and the ground masala and stir well. Boil well for around 10 minutes.
Add the toor dal and salt. Stir well and simmer for 5-6 minutes.
Heat oil in a tadka pan and add mustard seeds, red chillies and asafoetida. When crackling, add curry leaves and pour into sambar. Garnish with coriander leaves.