Take the minced veal out of the fridge half an hour before preparation. Preheat the oven to 180°C (356°F).
For the béchamel sauce: melt butter in a pan, add the flour while stirring, keep stirring until roux is cooked. Add milk while stirring, and add little by little. Keep stirring, let the sauce thicken slightly and season with nutmeg, pepper and salt. Let the sauce cool down. If too thick, add some milk, stirring.
Preheat a wok pan or skillet, add 2 tablespoons of oil and fry the veal mince loose. Add the tomato sauce. Season to taste with pepper and salt to taste. Let it cool down. Grease an oven dish with olive oil. Cover the bottom of the dish with lasagne sheets. Divide 1/4 of the mince mixture, divide the zucchini slices and cover with lasagne sheets. Then divide 1/4 of the mince mixture and pour over half of the béchamel sauce. Cover with lasagne sheets. Distribute 1/4 of the mince mixture, spread the basil leaves, keep the number of leaves for garnish, spread the remaining béchamel sauce, cover with lasagne sheets. Finally, divide the remainder of the mince mixture and the mozzarella over it, cover with Parmesan cheese. Put the dish in the oven for about 30 minutes. Garnish with basil.