Heat oil in a pan and add mustard seeds, curry leaves, cumin seeds to it. Let it splutter.
Add chopped onions ,green chillies, ginger and let it cook until onions are pink.
Now, add chopped leaves to it and cook until they wilt.
In a mortar and pestle, grind coriander seeds/ powder with coconut.
Add coriander powder- coconut mixture to the pan and mix well.
Add a spoonful of tamarind paste and mix well.
Heat oil, toast some garlic and red chillies. Add the tempering to the saag.
Serve hot with roti or rice.