Preheat the oven to 190C/170C Fan/Gas 5. Grease an ovenproof dish and a sheet of foil large enough to cover it. Cook the pasta for 2 minutes less than instructed. Drain.
Cook the onion in the oil until soft. Add the garlic and mushrooms. Cook until the juice runs out of the mushrooms. Increase the heat and continue to cook until most of the juices have evaporated. Add the passata and 1 1/2tsp of the oregano. Simmer, covered for 5 minutes. Set aside.
Mix the mince with a third of the breadcrumbs, the tomato ketchup, and the rest of the oregano. Shape into 12 mini meatballs. Heat the oil in a frying pan and cook until brown on all sides.
Add the meatballs to the sauce and simmer for 5 minutes. Stir in the pasta.
Turn into the ovenproof dish. Cover with the foil and bake for 10 minutes. Remove the foil and sprinkle on the rest of the breadcrumbs and the mozzarella and Parmesan. Bake for another 10 minutes.