Peel the onion and cut into fine cubes. Heat the oil and fry the onion for about 4 minutes while stirring. Add tomatoes, bring to the boil and season with salt, pepper and sugar.
Cabanossi cut into slices. Clean broccoli, cut into florets from the stalk, wash and slice. Peel, wash and slice the potatoes. Brush casserole dish with oil.
Mix the potatoes, broccoli and cabanossi and fill into the casserole dish. Pour sauce over it and sprinkle with cheese. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for 30-40 minutes.