Bring a large pot of well-salted water to a boil and cook the spaghetti al dente.
In the meantime, wash and dry the arugula. Then put it in a tall bowl with the cashews, basil, olive oil and salt. Blend thoroughly with a hand blender until you get a nice creamy pesto.
Now add a little pasta water to the pesto and mix well.
Once the pasta is cooked, drain and return to the pot. Immediately add the pesto and mix everything thoroughly.
Last but not least, transfer to deep plates. Using the zester grater, grate some of the lemon zest over each serving. Garnish with a few leaves of arugula and sprinkle with freshly grated parmesan to taste. Buon appetito!