Mix spinach, parsley and mozzarella cheese. Put the boneless pork (outer fat side down) on a wooden board and spread with the mustard. Spoon the spinach, parsley and mozarella cheese into the center of the bottom piece of loin.
Place the chopped ham on top of the spinach. Place the second piece of pork loin on top, tie securely with string to take on a “rolled” position and season with salt and pepper.
Place the loin on the open rack of a roasting pan and roast 1 – 1½ hours at 180°C.
Remove from oven and put somewhere in a warm place to “rest” for a few minutes. Remove the string and carve into 2 cm slices against the grain.