Heat 1 tbsp oil in a wide pan. Add all dals, mustard seed, asafoetida powder, dry red chillies, green chillies and fry till dal turns golden and spices and chillies are fragrant. Remove from heat and keep aside.
Add a little more oil to the same pan, if required, and add chopped onions. Cook till it turns golden.
Combine all fried items with coriander leaves, tamarind, and salt to a smooth consistency. Add water only if required.