Place the pork fillets between 2 sheets of lightly greased clingfilm and bash with a rolling pin until half their original thickness and almost doubled in size. Place the beaten egg in a shallow bowl. Mix the breadcrumbs with the parsley on a plate and season with pepper.
Dip the pork escalopes into the egg to lightly coat and then lightly coat in the herbed breadcrumbs.
Heat the oil in a large, heavy-based frying pan and cook the pork, in batches if necessary, over a high heat for 1–2 minutes on each side until the breadcrumbs are pale golden. Transfer the pork to a large baking sheet and arrange a slice of prosciutto on top of each and then a slice of Gruyère.
Place in a preheated oven, 200°C (400°F), Gas Mark 6, for 10 minutes until cooked through and the cheese is melted. Serve with a simple green salad and crusty bread, if liked.