For the sauce, wash the cherry tomatoes. Peel and finely dice 1 onion and garlic. Wash oregano, shake dry, remove leaves from the stalks and chop. Heat 2 tablespoons of oil and fry onion and garlic for about 3 minutes until translucent.
Add canned tomatoes, bring to the boil and simmer for about 10 minutes. After about 5 minutes of cooking time add cherry tomatoes. Season to taste with salt, pepper and oregano.
Cook the pasta in boiling salted water according to the instructions on the packet. For the mince, peel the remaining onion and dice very finely. Knead minced meat, onion, breadcrumbs, 4 tablespoons water and mustard. Season with salt and pepper.
Shape into about 12 meatballs. Heat 4 tablespoons of oil in a frying pan and fry the meatballs for about 5 minutes, turning them over.
Spread the pasta, sauce and meatballs in a greased casserole dish and sprinkle with cheese. Bake in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) for approx. 20 minutes.
Remove from the oven, sprinkle with oregano leaves if necessary.