Heat the oil in a large frying pan and cook the onion for 1 minute, then add the mince and cook for a further 5 minutes, until lightly browned. Add the sweet potato and cook for 5 minutes, adding the pine nuts for the final 2 minutes. Add the passata and tomato purée and simmer for 15 minutes, until reduced to a thick sauce. Season with freshly ground black pepper, then stir through the spinach and set aside to cool. Drain the mozzarella ball, tear into pieces and stir into the cooled mince.
Preheat the oven to 200ºC, fan 180ºC, gas 6. Lightly oil a baking tray. Make up the pizza base mix according to pack instructions. Divide the dough into 4 pieces, then knead each into a ball on a lightly floured surface. Roll out into circles, each measuring about 18cm in diameter.
Using just half of the mince mixture (see tip on what to do with the rest), spoon a quarter of it into the middle of each circle. Brush the edges of the dough with a little water, fold over to form a crescent and crimp the edges together with your fingers to seal.
Brush the tops of the calzones with the beaten egg, then bake for 20 minutes, until golden and heated through. Serve with the rocket salad on the side.
Cook't tip: this recipe makes 8 calzone. If you don't need them all at once, freeze the extras uncooked. Cook from frozen at 200ºC, fan 180ºC, gas 6 for 30-40 minutes, until piping hot.