Fry the onions and cinnamon, until the onions are soft.
Add the potatoes, salt and stir-fry the potatoes for about 2 minutes.
Add some water, cover the pan and simmer until the potatoes are tender.
Heat the remaining oil over medium heat in a heavy bottomed wide pan.(A non-stick or cast iron pan is ideal as the liver needs to be stir fried over high heat.)