Heat the oil in a saucepan and gently fry the shallots for 5 minutes or until soft and just beginning to colour. Add the apples, lemon juice and apple juice and heat until bubbling. Cover the pan with a lid, reduce the heat to low and cook very gently for 5 minutes.
Stir in the sugar and allspice, increase the heat to medium and cook, uncovered, stirring occasionally, for 8–10 minutes until most of the liquid has evaporated and the apple is very tender and just beginning to break down.
Using a potato masher, partly mash the apples until they are semi-smooth but retain some of the chunky texture. Set aside until cool.
Cut the bread open lengthways, keeping it still attached along one side like a hinge. With the baguette opened out flat, thickly spread both sides with the apple sauce. Fill with the sliced pork and watercress, then close up and press together. Slice across the loaf into two portions, then cut each portion in half again for serving.