Peel and chop the onions. Peel the garlic cloves. Wash and roughly chop the tomatoes.
Heat oil in a pan over medium flame. Sizzle chana dal and urad dal.
Add 3 dry red chillies and saute for about 30 seconds.
Add chopped onion and garlic cloves. Sauté until the onions turn translucent, about 5 minutes.
Add the chopped tomatoes, tamarind paste and salt.
Mix well and cook covered till the tomatoes turn mushy.
Turn off the gas. Allow the mixture to cool slightly. Transfer it to a blender and grind to a smooth consistency. Add 1-2 tbsp water, if required.
Transfer the tomato onion chutney into a serving dish.
For the tempering, heat a little oil in a small pan. Add curry leaves, asafoetida, mustard seeds and urad dal. Saute for a few seconds.
Pour this tempering over the tomato onion chutney.
Serve Tomato Onion Chutney with Idli or Dosa.