Pressure cook tur dal, shallots, green chilly, turmeric powder and asafoetida with enough water to 3-4 whistles. Mash them slightly.
Heat little oil in a kadai, saute grated coconut, coriander seeds, red chilli, curry leaves, fenugreek seeds and cumin seeds. Roast them till coconut turns reddish brown. Grind it to a smooth paste.
To the cooked dal mixture, add roughly chopped tomatoes, the ground masala, tamarind water and salt. Add water to adjust consistency and give it a boil.
Season with crackled mustard seeds and red chilli. Top it with freshly chopped coriander leaves.