Cut the tortilla wraps in half horizontally and toast in the oven until crisp. Fry the onions in a saucepan over a low heat in the olive oil for about 10 minutes. In the last 2 minutes, add the chopped sage. Roughly chop the tomatoes and add them to the pan with a generous pinch of salt and the parsley; continue to cook over low heat until the tomatoes have broken down to a thick sauce, adding some water to loosen the mixture and prevent sticking. 

Cover the bottom of an ovenproof dish with a layer of the tortilla wraps and spoon enough lamb bouillon to moisten the tortilla wraps and enough tomato sauce to cover it. Layer a few slices of the prosciutto and mozzarella over the sauce. Continue to layer the tortilla wraps, stock, tomato sauce, prosciutto and mozzarella in the dish until they are all used up, finishing with a layer of tomato sauce. Sprinkle the top generously with the pecorino and sage leaves. You can also grind some pepper. Serve warm.