Heat the oil well in a non-stick pan. Sweat the zucchini grated and the onion cubes well. Season with salt and simmer covered over a low heat for about 10 minutes (the zucchini draw water).
Add the cream cheese, tzatziki and parsley to taste. Season to taste with salt and pepper. Bring to the boil again briefly and leave to stand on the switched-off hotplate for another 10 minutes.
If the sauce is too thick for you, you can dilute it with water, milk or cream.