This is the dish that quietly uses up whatever zucchini didn't make it into anything else that week, and nobody in this family has ever apologized for serving it as dinner rather than breakfast, which is apparently only a rule in other countries.
Serves 4.
Warm a generous amount of olive oil in a wide pan, and cook the zucchini and onion slowly over medium-low heat, stirring occasionally, until soft and lightly caramelized at the edges, fifteen to twenty minutes. Season with salt and pepper.
Beat the eggs with the Parmigiano, a pinch of salt, and the herbs if using. Pour the eggs over the vegetables in the pan, and stir gently just once or twice to distribute them evenly. Cover, and cook over low heat until the eggs are mostly set but still a little loose on top, eight to ten minutes.
To finish it the traditional way, slide the frittata out onto a large plate, invert the pan over the top, and flip the whole thing back into the pan so the uncooked side faces down. Cook for another minute or two, until fully set. If that feels like more than you want to attempt, a minute or two under a hot broiler does the same job with less drama.
If the frittata turns out rubbery instead of tender, it cooked too hot and too fast; eggs want low, steady heat throughout, not urgency. If it weeps water onto the plate, the zucchini wasn't cooked down enough before the eggs went in, and released its moisture into the eggs instead of into the pan beforehand. And if it falls apart during the flip, the bottom wasn't fully set yet; give it another minute covered before attempting it, and don't rush the one step in this recipe that actually rewards patience.