Peel and dice the potatoes and zucchini.
Boil for 20 min and drain.
Mash the potatoes and incorporate the cream and butter.
Add the zucchini dices to the mash, season and mix gently.
Preheat the oven to 200°c.
Cut the tomatoes into small cubes, chop the onion and fry in a pan with a drizzle of olive oil.
Add the tuna and season.
Butter a gratin dish, spread the first half of the mash on the bottom of the dish, sprinkle with half of the Mozzarella Maestrella, spread the tuna filling then cover with the remaining mash.
Sprinkle again with Mozzarella & Smoked provola Maestrella and bake for 20 min.