Wash the zucchini and cut them into strips using a potato peeler. Season with salt.
Arrange them in an oven dish and bake briefly, enough to soften them.
Saute the finely chopped onion in oil. Add the mince and cook until ready. Lay out this stuffing onto the zucchini strips. Wrap them into rolls and stick toothpicks through them, to keep the rolls from unrolling.
Arrange them in an oven dish, smeared with oil. Put a piece of mozzarella in each opening and bake until ready.