Whisk yogurt with water and keep aside.
Heat oil in a pan. When the oil is hot, add mustard seeds, fenugreek seeds, cumin seeds, and red chilies, and let them crackle for 4-5 seconds.
Add curry leaves, ginger, garlic, and green chilies and saute for 8-10 seconds.
Add shallots and fry until they turn slightly brown in color, stirring frequently.
Now add turmeric powder and mix well. Switch off the heat.
Now add the yogurt mixture to the pan and mix well. Switch on the heat again at low.
Cook the curry till it just starts to boil, stirring continuously to avoid it from curdling. Do not let the curry boil otherwise it will split. Switch off the heat. Add salt and mix well. Check for salt and add more if needed.