How to prepare Burger (patty): Deskin the yam and wash and cube them nicely. Deskin the bananas and slice them as well. Wash the chana dal. Crush the garlic cloves in a mortar-pestle. Now in a pressure cooker, add the yam, chana dal, raw banana, garlic, 1/2 tsp. salt, ginger and xbd cup water and pressure cook on high for one whistle and then simmer the flame, and cook till another two whistles. Let it cool and then crush to paste with a potato masher.