Preheat the oven to 375°F.

On a lightly floured work surface, roll out the dough to a round about 14 inches in diameter.

Transfer the dough round to a 9-inch springform or regular cake pan (line with parchment if using a regular cake pan), pressing into the bottom and up the sides about 2 inches. Using a knife or scissors, trim any overhang.

Place a sheet of parchment paper inside the dough and fill it with pie weights or dried beans. Bake until the sides are set and the top is starting to brown, 20–25 minutes. Remove it from the oven and remove the pie weights and parchment. Return the crust to the oven to continue to brown on the bottom, another 10 minutes or so.

Meanwhile, thinly slice a few coins of the zucchini to scatter over the top at the end (just a few pieces; this is purely for decor). Coarsely grate the rest on a box grater (or food processor attachment, if you can find it) along with the onion. Transfer both to a large bowl, season well with salt, toss, and let sit for 10–20 minutes, letting the water come out as the zucchini softens.

Once the crust is baked, remove it from the oven and set it aside while you prepare the filling. Using your hands (or a cheesecloth or kitchen towel), squeeze all the water from the zucchini/onion mixture (there will be a lot!). The zucchini/onions should be rather dry by the time you’re done with them.

In another large bowl, whisk the feta, eggs, and heavy cream together until well blended (some pieces of feta are fine). Add the zucchini/onion mixture and the greens and season well with salt and lots of pepper.

Pour the mixture into the prebaked quiche shell and scatter the top with the sliced zucchini coins and zucchini flowers, if available. Drizzle with olive oil and give it another crack of pepper and sprinkle of salt.

Bake until the custard is set and no longer jiggles, 40–45 minutes. It should look slightly puffed and browned around the edges, but still pretty blond in the center.