Roughly grate the zucchini and mix in a bowl with salt (about 1/2 teaspoon). Let stand for a while until the zucchini have drawn water. Don`t pour off! Gradually mix in all the other ingredients. Finally dust the flour over it. Put in a baking dish. Bake at 170 degrees fan-assisted or 200 degrees top / bottom heat for about 40 minutes.
A tomato sauce tastes good with it. The gratin also tastes cold!