Preparation:

1. Combine the flour and cold fat cut into pieces in a bowl, stirring until a crumbly mixture forms. Add the salt and half the water and knead the dough, gradually adding the remaining water. Stop adding water once you have a soft dough (depending on the quality of the flour, you may need to add a little less or a little more flour). Shape the dough into a ball, cover with plastic wrap and let rest.
2. Meanwhile, cut the tomatoes into cubes, place them in a bowl and season with olive oil and chilli to taste.
3. Once the dough is left to rise, cut it into 4 pieces and shape into balls. Lightly flour and roll the dough with a rolling pin until very thin. Cut out circles, each a few millimetres thick. Cook a piadina for a few minutes on each side, in a non-stick pan (the piadina is ready to turn when golden bubbles form on the side towards the bottom of the pan). Keep the cooked piadini hot in an oven preheated to 80°C.
4. Spread each piadina with a layer of cheese "squacquerene," then add the arugula leaves, marinated tomatoes and Rio Mare Insalatissime tuna salad. Fold in half and serve immediately.