For the tomato sauce, peel and finely dice the onion and garlic. Heat the oil in a pot. Fry the onion and garlic in it. Add tomatoes and tomato paste and let it boil down for about 10 minutes at medium heat.
Season with salt and oregano. Clean and wash the zucchini and eggplant, dab dry and cut into slices of about 1/2 cm thick. Peel garlic and crush finely. Mix garlic, oil and lemon juice.
Season with pepper. Brush the zucchini and eggplant slices with the oil. Put the vegetables on a baking tray and grill them for 3-4 minutes on each side. Wash the basil and cut into strips. Cut mozzarella into slices.
Grease a casserole dish (approx. 22x22 cm) with oil. Spread a thin layer of tomato sauce evenly on the base. Cover with pastry sheets. Place aubergine slices on top. Cover with mozzarella (keep 3 slices).
Place further lasagne plates on top. Cover with the zucchini slices. Spread some tomato sauce on top and sprinkle with basil. Cover with the remaining pastry plates. Spread the remaining tomato sauce and mozzarella on top.
Sprinkle with parmesan. Cook lasagne in the preheated oven (electric: 200 °C/ gas: level 3) for 30-35 minutes. Cut ham slices in half and leave them crisp in a pan without fat. Remove the lasagne, let it cool down for 5 minutes, cut it into pieces and garnish with ham and basil leaves.