Thaw the spinach, squeeze out the liquid and roughly chop. Peel and dice the onions.
Heat 2 tbsp olive oil in a pan and fry the onions over a medium heat for 2 minutes until translucent. Add the spinach and cook for a further 4 minutes. Season the spinach with salt, pepper and freshly grated nutmeg. Allow to cool.
Separate the eggs. Coarsely grate the mozzarella. Mix the egg yolks with the ricotta, grated cheese and spinach. (The egg whites are not needed in this dish.)
Cut the cold cuts into fine strips.
Drain and chop the sun-dried tomatoes.
Divide the pizza dough into quarters, roll out to 22cm circles, about 1cm thick, and place on a baking tray lined with baking paper.
Cover half of each pizza with the spinach and ricotta mixture and sprinkle with the meat strips and tomato cubes.
Fold the plain pizza halves over the filling and press the edges tightly with a fork.
Brush each calzone with some olive oil and bake in a preheated oven at 220°C (200°C fan, gas 7) for 20-25 minutes.