Instructions:

1. Peel and finely chop the onion.
   
2. Heat a little olive oil in a pot over low heat. Add the onion and sauté until soft.
   
3. Add the tomato purée, 100 ml of water, a pinch of salt, and a pinch of sugar. Simmer over low heat for 45 minutes, stirring occasionally. Once done, remove from heat and add a few basil leaves.
   
4. While the tomato sauce is cooking, dice the mozzarella into small cubes and place them on a clean kitchen towel lined with paper towels. Let sit for 30 minutes to drain excess moisture.
   
5. Meanwhile, wash and trim the zucchini. Slice them into 3–4 mm (1/8 inch) thick slices.
   
6. Cook the zucchini slices by either frying them in olive oil or, for a lighter option, baking them in a preheated oven at 180°C (350°F) for 10 minutes per side (8–9 minutes at 160°C/320°F if using a fan-assisted oven).
   
7. Lightly grease the bottom of a baking dish with some tomato sauce.
   
8. Layer the zucchini slices and sprinkle lightly with dried mint and black pepper. Cover with tomato sauce, add some mozzarella, and sprinkle with grated Parmesan. Continue layering until all ingredients are used.
   
9. Generously top the final layer with Parmesan.
   
10. Bake in a preheated oven at 180°C (350°F) for 40 minutes (35–40 minutes at 160°C/320°F if using a fan-assisted oven). Let cool slightly before serving.