Blanch kale in a large pot of boiling salted water, about 1 minute. Dunk in ice water to stop cooking process; wring dry in a clean kitchen towel. Transfer to a food processor, add garlic, Parmesan, and walnuts, and pulse until coarsely chopped. With motor running, add oil in a steady stream and process to a coarse purée. Add lemon juice and season with salt and pepper.