Lay a sheet of plastic wrap out on a work surface. Place a piece of veal on the plastic, and cover with another sheet of plastic. Pound the meat with a meat pounder or other flat utensil until it is uniformly 1/8 inch thick. Repeat with remaining pieces. (The butcher could also do this step.)
Lay the veal out on the work surface. Top each piece with a slice of prosciutto and then a slice of cheese. Fold the veal over to completely enclose the prosciutto and cheese and secure with toothpicks. You should have nice little flat pachages about 3 by 2 inches. Sprinkle both sides of the veal with salt and pepper, to taste. Place the flour on a small plate and dredge the veal packages in the flour, shaking off any excess.
Heat the butter and oil in a large skillet over medium-high heat. When the butter foam subsides, add the meat and brown on both sides, turning as necessary. Reduce the heat if necessary to keep the veal from burning. When the packages are golden brown, transfer them to a heated plate.
Add the Marsala to the pan juices and stir well to release the browned bits on the bottom of the pan. Reduce the heat to low, return the veal to the pan, and simmer for 2 to 3 minutes, with a lid slightly ajar, until the meat is tender and cooked through. Return the veal to the heated plate. Add the lemon juice and parsley to the pan, increase the heat, and cook for 1 minute, or until the sauce has thickened.
To serve, remove the toothpicks and serve 2 little suitcase, drizzled with the sauce, per person. Serve immediately.