This is the basic recipe for Avgolemono, the sauce in turn can be poured over stuffed zucchini and is also used in a chicken soup and a soup known as Youvarlakia (meatball soup/egg/lemon soup)
(Avgo means egg in greek)
Beat the egg yolks and lemon juice. (Save egg-whites for another dish)
Remove some of the broth from whatever you're finished cooking.This sauce is added in the last 5 minutes. (Boiling chicken, meatballs, zucchini) and gradually add it to the beaten egg yolks. You want to increase the temperature without ending up with omelette!
Add the beaten egg mixture back to the pot, do not stir the soup, simply gently shake the pot to distribute the mix. Do not let it boil. It will start to thicken and will be ready in five minutes.
You can add more lemon, salt/pepper now if you want.