Put the nuts and herbs in the food processor and whiz up. The mixture will be fine, but should still have texture, not be completely pulverized.
Cook the spaghetti in boiling, salted water until al dente. Drain. Toss in a bowl with the nuts (reserving some for garnish), olive oil, cheese, and orange zest, to taste, if using. Serve immediately.
Recipe courtesy of Laura Calder