Soak the bun in lukewarm water, press well, crush and mix with the minced meat in a bowl. Make a well in the centre, add the egg and spread the parsley over the edge.
Drain the olives and tomatoes. Cut with the mozzarella into small cubes. Mix the olives, tomatoes and mozzarella. Preheat the oven to 200°C (180°C fan, gas 6).
Knead the minced meat mixture to mix and season with salt and pepper. Divide into small portions. Press each portion flat and place 1 tsp of the filling in the middle. Shape the mince around to enclose the filling and form meatballs.
Pour the flour on a plate and season with a little salt and pepper. Turn the meatballs in it to coat. Pat gently.
Place on a baking tray lined with baking paper and bake in the preheated oven for 25-30 minutes, turning halfway through.