In a wide saucepan, add a little olive oil and the beef, in thin slices. Do not stir. Cook until golden brown.
Cut the onion, carrot and celery in thin slices, and add to the saucepan. Stir. Add the chopped tomatoes, a little water, salt, sweet paprika, and stir. Close the saucepan, lower the heat and cook for at least 2 hours.
After the mixture is cooked and has absorbed its liquids, add the basil, minced, and stir vigorously in order to “break down” the meat, to become a uniform mass.
Let it cool down a little.
Preheat the oven at the max. temperature.
Cut the crust in half, fold it and cut off the edges to give a circular shape.
Flour a baking pan. Lay the crust, cut the mozzarella into bits with your hands and sprinkle over it towards the center, pour over the stuffing and cover the baking pan.
Press strongly the edge with a fork to seal it and open a hole in it.
Bake at 280oC for 5 min.
In a bowl, mix the yoghurt, mayonnaise, lemon juice, a little olive oil and salt.
Cut the calzone in half and serve with yoghurt and a little arugula.