For the Pesto:
Bring a pot of water to a boil.
Place the kale leaves in the boiling water and cook until bright green, about 1 minute. Drain and rinse with cold water to stop the cooking process, then place the kale on a kitchen towel to dry.
To the bowl of a food processor or blender, add the garlic, parsley, parmesan, toasted walnuts, lemon zest, lemon juice, red chili flakes, salt and pepper. Pulse until coarsely chopped. Add in the kale and yogurt and pulse a few more times.
With motor running, add the oil in a steady stream and pulse to a coarse purée. Taste and adjust seasoning. Cover and refrigerate until ready to use, up to 3 days. Pesto yields approximately 1 ½ cups.
Bring a large pot of salted water to a boil and cook 8 oz of pasta until al dente. Reserve ½ cup of the cooking liquid. Drain pasta and return to pot. Toss with ½ to ¾ cup pesto and the reserved pasta water.
Garnish with freshly grated parmesan cheese and serve warm.