Drain the tomatoes and peel the onion, finely chop both. Finely chop the parsley. Heat the oil in a frying pan. Sauté the tomatoes, onion and half of the parsley for approx. 5 mins. Remove, transfer to a bowl, allow to cool slightly. Set aside the remainder of the parsley.
Add the mince, breadcrumbs and salt, mix and knead well until the ingredients have combined to form a compact mass. Divide the mixture into 20 portions and shape into balls with wet hands.
Heat the oil in the same pan. Turn down the heat, fry the meatballs in batches over a medium heat for approx. 7 mins. all over. Remove and set aside.
Heat a dash of oil in the same pan. Fry the gnocchi for approx. 5 mins., stirring occasionally, remove and set aside.
Press the garlic clove. Heat a dash of oil in the same pan, briefly sauté the garlic. Add the tomatoes and the reserved parsley, season and simmer for approx. 10 mins., stirring occasionally. Tear off the oregano leaves, add to the sauce along with the meatballs and gnocchi, mix.
Top with the mozzarella, cover and simmer for approx. 5 mins. until the cheese has melted.