Pre-heat oven to 180°C.
Open up the roast to form a flat piece of meat and cut it on the inside to even out if necessary. (Your butcher can do this for you.)
Spread mustard inside the roast and arrange slices of ham on top of the mustard. Arrange the mozzarella slices or balls down the centre of the piece of pork. Arrange a row of prunes next to the cheese.
Roll the piece of pork up so that the prunes are in the center, or fold over to form a “pocket” where the prunes are inside.
Secure with string to keep a neat shape and to hold the stuffing inside.
Rub outside of roast with olive oil. Place on open rack of oven roasting pan and roast approx. 1 hour and 50 minutes. Remove string and leave in a warm place for 5 – 10 minutes to “rest” and allow the juices to settle.
Carve in thin slices and serve with gravy and steamed vegetables.