Take a liquidiser jar. Put Curd, milk, water, both salt, cumin - chilly powder, ginger, mint leaves in the jar.
Now blend all ingredients on low to high speed for one minute. Add some ice cubes as per your preference.
Heat oil in a small pan on medium heat.
Add mustard seeds, green chilies and curry leaves for 30 seconds. Switch off the gas stove.
Add this temper into lassi mixture and mix very well.
Pour lassi into glasses and just beat the heat with this refreshing lassi.