Start preparing the bechamel sauce. In a saucepan, let the butter melt over moderate heat; add the flour mixing with the whisk. Then pour the cold milk and continue to stir until it starts to boil. Salt, decrease the intensity of the flame and cook for at least twenty minutes covered and stirring occasionally. Remove from the heat, adjust if you need salt and, if desired, season with a pinch of nutmeg or pepper. If the bechamel is too thick, you can add a little milk. If it is too liquid, put on the heat adding a knob of butter. Cool the sauce for about 15 minutes before using. It becomes firmer as it cools.
Wash and dry the zucchini. Remove the ends, then slice them into very thin slices. Put them on a plate and sprinkle with a little salt and pepper. Cut the mozzarella into cubes and prepare the slices of baked ham.
Take a baking tray and wet the bottom with a drizzle of extra virgin olive oil. Spread 3-4 tablespoons of bechamel on the bottom, lay the the lasagna sheets, then cover with the zucchini slices. Distribute the mozzarella cubes and the sliced baked ham, then add the béchamel and a sprinkle with grated parmesan cheese. Continue alternating the pasta sheets, béchamel sauce, zucchini, mozzarella and baked ham until you complete the tray.
Complete with a layer of bechamel and sprinkle with parmesan cheese. Bake at 480F (250°C) for about 30 minutes, check cooking and when ready you can serve hot white lasagna zucchini and ham.