Peel and wash the potatoes. Zucchini clean, wash and halve long ago. Cut potatoes and zucchini into longish slices. Cut cabanossi into equally thick slices. Heat oil in a pan.
Fry the potato and zucchini slices one after the other in the pan until golden brown, season with salt and pepper. Fry the cabanossi in the pan on both sides. Peel the garlic and press it through a garlic press.
Stir into the tomato sauce. Spread the tomato sauce in the casserole dish and place a layer of potatoes in the dish. Pour a little tomato sauce over the potato slices and place a layer of courgette on top.
Cabanossi slices on it distribute and again some sauce over it give. Layer the remaining zucchini and potato slices in the same way. Spread crème fraiche on the top layer and cover with the cheese.
Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for about 20 minutes. Garnish casserole with oregano.