Halve the zucchini, remove the core, cut the zucchini into slices.
Cut the onions into slices and cut the tomatoes into eighths. Put the oil in a pan and let the onions become translucent, then add the zucchine slices and simmer over a medium heat for about 8-15 minutes (depending on the thickness of the slices). Finally add the tomatoes. Season to taste with pepper and salt and let cook a little more.
A butter sandwich tastes best with it, but it is also good as an accompaniment to lunch.