At first, boil the paccheri in plenty of salted water and drain them "al dente".
Stri-fry the cubes of San Daniele ham with onion and tomato cubes; then, stirring, add the béchamel sauce and the parmesan.
With a pastry bag, stuff the paccheri and place them vertically on a sheet pan, creating four shapes with the slices of San Daniele ham. Tie them with cooking twine.
Bake the paccheri for 10 minutes at 195°C.
Top with pepper and serve the paccheri gratin with tomato cubes on each serving plate.