Heat 1 tsp oil and saute 1 tsp ginger, 1 tsp garlic and green chillies and then add 2 tbsp onions.
Add mashed yam and mix well with some salt, tsp cumin powder, 1 tsp garam masala, lemon juice and green coriander .
Once yam is cooked well add little oats powder and mix again. Let it rest in refrigerator for 15 mins.
Now make small balls and cook on slow flame with some oil in appe pan. You can also deep fry if you fine with that.
For the gravy, heat 1 tbsp oil and saute onions with ginger garlic paste for 2 mins.
Add tomato puree and cook till the masala is all done.
Add turmeric powder, coriander powder, red chilli powder and salt and cook it for another 1 min. Masala will leave oil and would become one lump.
Add kasoori methi and some water for the gravy. Mix the masala well and let it come to boil.
Now serve the yam balls in a serving dish and pour the gravy over it and then garnish with fresh coriander and serve with rice or roti.