Brown a sliced onion in some extra virgin olive oil until translucent. Next add sliced zucchini and sauté until golden. While your pasta cooks in plenty boiling water, grate your parmesan and if you like also a small quantity of pecorino cheese. Add to this freshly ground black pepper, and an egg yolk. Whisk together to obtain a rather liquid, creamy sauce. Drain the pasta and toss it in the zucchini pan, mixing to coat well. Take off the stove and pour in the eggy mix while still blending it all together. Serve dusted with more grated cheese.