Peel and dice the raw mangoes. Add it into a mixer or food processor and grind it to a smooth puree along with mustard seeds, green chillies, garlic clove, turmeric powder and salt as per taste .
In a large bowl, add the whisked yogurt and the pureed mango mixture. Stir and mix well by hand till it the mango puree is well blended in the yogurt. You may add water as per your required gravy consistency.
Prepare the tempering. Heat a pan and add oil into it. Add asaefoetida and mustard seeds. When the cracking sound stops, add the urad dal, red chillies and curry leaves. Saute on low flame till the urad dal turns light golden.
Add the tempering into mango yogurt curry. Serve it as a side dish with rice.