Cook pasta in a large pot of boiling, salted water until just tender. Meanwhile, heat the olive oil in a large skillet set over medium-high heat. Add the onion, garlic, sun-dried tomatoes and chili flakes and cook until the onions are just tender, about 3 to 4 minutes. Add the kale and stock and bring to a simmer. Reduce heat to medium-low. Strain the pasta, reserving 1/2 cup of the cooking liquid. Add the pasta, reserved cooking liquid, feta cheese, salt, pepper and parsley to the skillet and toss to combine. Serve immediately.
Note: To blanch the kale, plunge into boiling water and cook 2 to 3 minutes. Remove and cool in cold water. Drain well, squeezing as much moisture out of the kale as you can.