Heat a pan with oil, add cumin, mustard and curry leaves.
Let the spices begin to splutter, then add hing, green chilies, potatoes and peas. Fry for around 2 to 3 mins.
Add enough water to cover the potatoes and allow them to soft cook.
While the potatoes cook, make a fine powder of the fried gram in a mixer.
Add little water just enough to make a thick paste of the gram flour. It must be of pouring consistency. Add salt and turmeric to the paste.
When the potatoes are cooked, pour the mix and stir well to prevent lumps. Simmer the gravy till it thickens. Switch off the stove.
Add lemon juice and mix well. Garnish potato sagu with coriander leaves.