Finely chop (or puree) the basil and tomatoes and mix with the olive oil and salt.
Cut the mozzarella horizontally twice, distribute the basil / tomato mixture between the slices, put the cheese back together and wrap the ham slices tightly around it.
Wrap the parcel in cling film and put it in the refrigerator for about 3 hours.
Cut the peppers into small cubes, chop the parsley and spring onions (with a nice green color).
In a bowl with a whisk, stir both vinegar, mustard, olive oil, pepper and salt to a creamy sauce; Mix in the diced pepperoni, parsley and spring onions.
Carefully cut the mozzarella into 4 (or more) slices, arrange and spread the vinaigrette all around.
Change the basil / tomato ratio as you like; the paste should not be too thin (liquid)