Bring a large pot of salted water to a boil. Cook the pasta according to the package directions. Reserve about 2 cups of the starchy cooking water and drain the pasta. Return to the hot pot.
While the pasta is cooking, make the pesto. Place the pistachios and garlic in the bowl of a food processor fitted with a steel blade. Process until the pistachios are finely chopped. Add the lemon zest and juice, kale, and nutritional yeast. Process until everything is finely chopped. Add the flax seed and olive oils and pepper and pulse a few times to combine. Scrape down the sides of the bowl if needed. Taste and add salt if desired.
Add the pesto to the pasta with enough of the starchy cooking water to coat the pasta (add the water a little at a time until desired consistency is achieved).