Cut the onion into rings, the fennel bulb into 0.5 cm thick slices and cut the tomatoes in half. Finely chop the garlic and cut or break the dry bread or rolls into bite-sized pieces. Put everything together in the baking dish, season and mix well. Pour the tomatoes or the tomato sauce on top, cover with the sliced mozzarella and sprinkle with (freshly) grated Parmesan.
Bake in a hot oven for approx. 20 - 25 minutes at 200 ° C top / bottom heat.
A super-fast and delicious casserole that offers many options for further use of leftovers (e.g. pasta or rice from the day before, instead of bread, etc.).