Wash spinach 2-3 times in enough water to remove all the dirt .
Chop the hard stalks of spinach ,no need to remove the tender stalks
Peel and chop potato into medium size cubes (peeling potato is optional)
Heat oil in a pan ,a prefer to use a iron kadhai to cook spinach
Add mustard oil and let it heat properly and then switch off the heat and let it cool down slightly.
Now add cumin seeds ,chopped green chilies ,ginger and asafoetida.
Now add chopped potatoes and salt and mix.
Cover and cook on medium heat
Stir 2-3 times in between to avoid sticking to the bottom.
When potatoes are 90% done then add the chopped spinach and mix.
Cook on medium heat till spinach become soft (no need to cover the pan now)
When done add garam masala and lemon juice and mix
Serve hot with chapati or rice