Wash, salt, flour and fry the fresh sole in hot extra virgin olive oil. Then, in the oil left over from the frying, cook the sliced Tropea red onions for almost an hour over very low heat, with a little salt, cinnamon and a tablespoon of sugar, stirring the mixture often. When the onions are well browned, taste them and add, if necessary, more sugar, also pour a tablespoon of vinegar, a finger of water and boil for a few minutes. Take a bowl and put a layer of fish, which in the meantime will have cooled, one of onions, then again the fish, and so on until you run out of ingredients. Finish with the layer of onions and tomato sauce, let stand after a few hours serve.