Heat oil in a pan add chana dal,coriander seeds,garlic and red chillies, fry for 2 mins until fragrant.Add onion.
Add required salt and saute till transparent then add radish.Saute for 2 mins.
Cook covered for 5-7 mins in low flame.Take a piece of radish to check if its cooked cut with spoon and see it cuts easily then its perfect.Saute for 2 mins.Switch off and cool down completely.
Transfer to mixer jar.First grind it coarse, radish will let out water so add water accordingly.Grind to chutney consistency.
In a pan heat oil - add mustard seeds let it splutter then add urad dal and curry leaves saute till dal turns golden.Transfer tadka to chutney, mix well.
Serve with idli,dosa or oothapam and enjoy!