Make the Onion Filling: Heat 1tbsp oil in a saute pan on medium-high heat, add the curry leaves and onions. Cook till the onions begin to soften, about 5 minutes. Then stir in the crushed red pepper flakes, salt, sugar, tamarind, ginger and cinnamon. Continue to cook till the onions are very soft, about 10 minutes. Remove from heat and set aside.