Rinse the barley and put itin a large pot with plenty of cold water and boil for about 25 minutes after it has come to a boil (with a pressure cooker the cooking time is halved).
In the meantime, thinly slice the onion and wash, peel and dice the zucchini. Sauté the onion for a few seconds in a frying pan with a little oil, add the zucchini, salt and cook for 7-8 minutes, so that the vegetables remain a bit crisp.
Drain the barley, let it cool and add salt, then mix the zucchini; add the ricotta, the Parmesan, the finely chopped fresh herbs and the egg yolks. Beat the egg whites separately and gently fold them into the mixture. Adjust the salt and pepper and put everything into a rectangular cake mold lined with parchment paper that has been wetted and squeezed out, previously greased with a little oil. Cover the mold with aluminum foil and bake in a hot oven at 180°C (355°F) for about 50 minutes, removing the aluminum foil after the first 30 minutes.
Prepare the accompanying sauce by mixing the Greek yogurt with the quark or the spreadable cheese, the lemon, the extra virgin olive oil, a pinch of salt and freshly ground pepper, and complete with a few finely chopped chives. Keep cool until ready to serve.