Make the beef filling: Heat the olive oil in a large pan over medium-low heat. Add the onion and cook for about 2 minutes until softened and fragrant. Add the bell pepper and cook for another 2 to 3 minutes until softened. Add the minced beef and break it up with a spoon. Cook until it starts to brown. Season with salt, pepper, paprika and nutmeg, then mix well.
Stir in the tomato paste, passata and water. Reduce the heat to low, cover with a lid and cook for about 15 minutes, until the mixture is rich and thickened. Taste and adjust seasoning if needed. Remove from the heat, stir in the chopped coriander, then set aside to cool to room temperature.
Preheat the oven to 190 C fan.
Fold the parcels: Place one tortilla on a board and cut it in half to make two semi-circles. Working with one semi-circle at a time, brush a little water around the edges, then place a bit of mozzarella in the centre and add 2 to 3 tablespoons of the beef filling on top. Take one pointed corner and fold it over the filling, pressing gently. You will be left with a small flap. Fold the flap over the folded tortilla and press again to lock it in place. Press and seal the open seam by pinching the edges together, then fold that sealed edge slightly down. Think of it like folding a paper triangle that ends up as a sealed pocket. Repeat with the remaining tortillas, cheese and filling.
Assemble and bake: In a 22 cm (9 inch) round baking dish, mix the passata with dried parsley, salt and pepper. Scoop out 2 tablespoons of the sauce and set it aside for brushing. Spread the remaining sauce evenly in the baking dish, then arrange the tortilla parcels on top. Brush the parcels with the reserved sauce, sprinkle over the mozzarella, and bake for about 15 minutes, or until the cheese is melted and golden. Garnish with chopped coriander and serve warm.