Bring a large pot with about 4 cups of water to a rolling boil.
Switch off the flame.
Immerse the chopped spinach and slit green chilies in the water and keep covered.
After 5 mins, open the lid and drain the water completely from the spinach.
Let the spinach cool.
Once cool, blend the spinach, green chilies and salt to a smooth paste without adding any water. I used my immersion blender for this but any normal blender will work too.
Once blended, heat a pan with oil.
Pop the mustard seeds and immediately add hing and urad dal.
Once the dal begins to brown, add the chopped garlic and wait for it to brown.
When the garlic turns golden brown, add the tempering to the mashed spinach and mix well.
Serve hot with rice.