Toast the coriander, cumin, peppercorns, and fenugreek in a dry saucepan over medium heat until fragrant and lightly browned, about 5 minutes. Transfer to a bowl to cool, then crush to a coarse powder using a mortar and pestle or spice grinder. Mix in the turmeric and red chili.

In a large saucepan, combine the dal, tomato, garlic, tamarind, salt, ground spice mixture, and water. Bring the liquid to a boil, then remove from the heat immediately.

Heat the oil in a small saucepan over medium-high heat until it shimmers. Add the asafetida and mustard seeds. When the seeds begin to spatter, add the curry leaves and stir for a few seconds to release their aroma.

Pour the tempering into the large saucepan and stir well to combine. Taste and adjust the seasoning with more salt, red chili, or tamarind as needed. Serve piping hot, topped with cilantro.