Cook the mango pieces with turmeric, salt and enough water to cook the mango.
Mash it and keep it aside.
Grind together coconut, cumin seeds, green chillies and mustard seeds into a fine paste by adding little water.
Add the ground paste to the mashed mango and mix well.
Cook it again by adding little water, if necessary.
Add sugar and mix well.
:- Check the level of salt and add, if necessary.
When it becomes a paste like consistency, switch off the flame.
Heat oil in a small pan.
Splutter mustard seeds and fry curry leaves for a minute.
Add the above seasoning into the above mango-coconut paste.
:- Serve with rice.