Take a nonstick pan and heat with cooking oil. Then, add urad dal, chana dal, curry leaves, red chilies. Saute till it turns colour.
Next, add finely chopped tomatoes and add salt. Cook till the tomatoes are soft and well cooked. This takes about 10 mins.
Transfer to a plate and allow to cool.
Take the tomatoes along with coriander leaves and grind to a smooth paste and transfer to a bowl.
Heat a nonstick pan with cooking oil and add mustard, curry leaves.
When the mustard splutters, pout it over the chutney and serve with Dosa / Idli.