Prepare the meatballs: In a large bowl, combine the chicken or turkey mince, chopped onion, garlic, breadcrumbs, egg, oregano, smoked paprika, chilli flakes, salt, and black pepper. Mix gently until just combined.
Shape the meatballs: Roll the mixture into small meatballs, roughly the size of a walnut. You should get approximately 20–24 meatballs.
Brown the meatballs: Heat the olive oil in a large, deep ovenproof frying pan over medium heat. Add the meatballs in batches if necessary and cook for 5–7 minutes, turning regularly, until browned on the outside. Remove and set aside.
Make the sauce: In the same pan, add the diced onion and cook for 2–3 minutes until softened. Add the garlic and cook for another 30 seconds.
Add the tomatoes: Stir in the passata, tomato purée, Italian herbs, chilli flakes, and chicken stock. Season with salt and black pepper and bring the sauce to a gentle simmer.
Return the meatballs: Place the browned meatballs back into the pan and simmer gently for 8–10 minutes, allowing them to cook through and absorb the spicy tomato sauce.
Add the lasagne sheets: Tuck the broken lasagne sheets into the sauce, making sure they are mostly covered. Cover the pan and simmer for 10–12 minutes, stirring gently once or twice to prevent the pasta from sticking.
Add the cheese: Remove the lid and scatter the mozzarella and Parmesan evenly over the top.
Bake until golden: Place the pan under a preheated grill for 3–5 minutes, or transfer it to a 200°C oven for 8–10 minutes, until the cheese is melted, bubbling, and golden.
Rest and serve: Allow the lasagne to rest for 5 minutes before serving. Garnish with fresh basil or parsley and enjoy while hot.