Bring a large pot of salted water to the boil and add in the spaghetti or pasta. Cook according to packet instructions. Reserve ½ cup of the pasta water before draining the pasta.

Place the kale, walnuts, garlic, lemon and salt in a food processor with the olive oil and blend until everything starts to come together. Scrape down the sides of the food processor with a rubber spatula and continue to blend until the pesto reaches the desired consistency. Adjust salt and lemon juice to taste.

Add the cooked spaghetti back into the saucepan with a couple of tablespoons of the cooking water to loosen up the pasta. Add in the pesto and toss to combine. Add a little more of the cooking water as needed to help toss the pasta until every strand is covered with the pesto. Taste and adjust salt and lemon again as needed before serving.