Peel and finely chop the onion. Heat the oil in a pot and sauté the onion until transparent. Add canned tomatoes, chop with a wooden spoon and boil down for about 20 minutes until thick. Season with salt and pepper. Wash basil, shake dry, remove leaves and cut into strips. Keep some leaves for garnishing.
Add basil strips to the sauce. Wash the zucchini, grate dry and cut into slices. Brush the grill pan with oil, fry the zucchini slices in it, season with salt and pepper. Drain dried tomatoes on kitchen paper. Grate mozzarella roughly
Divide the tomato sauce into 4 ovenproof portion moulds (200 ml each). Spread zucchini slices and dried tomatoes in a fan-shaped circle. Sprinkle with mozzarella. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 15 minutes until the cheese has melted and is golden brown. Garnish with basil leaves