Heat 3/4 cup of the oil in a large, deep saucepan over medium-low heat. When hot, add the sliced onions and cook stirring until they soften. Add the cinnamon, lentils, and ginger to the pan and cook, stirring often, about 10 minutes. Add the stock and 5 cups hot water, salt to taste, and cayenne pepper. Bring to the boil, then simmer about 10 minutes. Add the lemon juice and squeezed shell and cook about 50 minutes longer, stirring often. Heat the remaining 1/2 cup oil in a small pan and add the chopped onion, garlic, chile, and bay leaves. Cook, stirring until the onion is browned. Add this mixture, including the oil, to the lentils. Sprinkle with the chopped coriander leaves and serve hot.