Boil up about 3 l salted water. Preheat oven (electric cooker: 225 °C/circulating air: 200 °C/gas: level 4). Clean and wash the broccoli and divide into florets. Peel and chop onion and garlic.
For the sauce, fry the onion and garlic in hot oil. Add tomatoes, bring to the boil. Season with salt, pepper, oregano and 1 pinch of sugar. Simmer covered for about 5 minutes.
Steam broccoli covered in little boiling salted water for about 5 minutes. Add the tortellini to the boiling salted water and cook for about 2 minutes (see also package instructions). Drain broccoli and noodles.
Cut the mozzarella into slices. Grease a large casserole dish.
Spread the tortellini and broccoli in the dish. Pour tomato sauce over it and spread mozzarella on top. Bake in a hot oven for about 10 minutes.