Wash the zucchini well, dry and cut into thin slices. In addition, put a large pot with water and when it begins to boil you must add the slices of zucchini in batches, to cook for about a minute. Take them out and cool them in a container with iced water to stop the cooking and let them drain on a kitchen towel.
Peel the garlic and onion and cut into squares. Put a dash of oil in a frying pan and sauté the vegetables until they start to brown. Add the crushed tomato and continue cooking for 7-8 minutes and then add the chopped veal and salt and pepper and cook until it is done.
For the bechamel: Melt the butter in a casserole and add the flour, toast for 2 minutes stirring continuously so that it does not burn. Add the warm milk, a little salt and freshly grated nutmeg and keep over medium heat without stopping stirring until it starts to cook and thickens. A few minutes before removing from the heat, add 1/3 of the grated cheese.
In a heat-resistant dish put a thin layer of bechamel, a layer of zucchini on top and then half of the meat, put another layer of zucchini, the rest of the meat and finish with zucchini. Finally, add the remaining bechamel sauce on top and sprinkle with the rest of the grated cheese.
Preheat the oven to 180 ºC, put the lasagna in and keep it until the surface is well browned.