Grind mango, coconut, red chillies along with salt, using little water as required. Transfer to a serving dish
Prepare the tempering (tadka/chaunk/baghar): Heat the oil in a small pan. Add in mustard seeds. When they splutter, add in urad dal and curry leaves. Fry for about 15-20 seconds till urad dal starts turning brown.
Turn off the gas and pour this tempering onto the chutney. Serve fresh with Idli, dosa and thalipeeth etc.
If you are not using coconut oil, use mustard oil or peanut oil but NO Olive oil or sunflower oil for this chutney would do. A dish like this needs an oil base with distinctive flavour to support the taste.