Cook the noodles in salted water according to the package directions until they are al dente, and reserve about 1/2 cup of their starchy cooking water before draining.
Meanwhile, in a food processor or blender, pulse the pistachios and 2 packed cups of the arugula until they are finely chopped.
Add the remaining ingredients and pulse until it is well blended but not too smooth (unless you prefer it that way).
Drain the noodles, toss them immediately with the remaining arugula and the pesto.
Slowly add the reserved pasta water to thin the sauce as needed.
Serve it immediately or refrigerate it for up to 48 hours.