Heat the oil in a large skillet over medium heat. Add the shallots, fennel, garlic, red pepper flakes, sage, ½ teaspoon salt, and freshly ground black pepper and cook until the fennel is tender, about 8 minutes.
Meanwhile, bring a large pot of salted water to a boil and cook the pasta until al dente.
To the skillet, add the white wine and let it reduce for 30 seconds. Then, reduce the heat to low, add the kale and toss until just wilted. Use a slotted spoon to scoop the cooked pasta into the skillet. Add the sun-dried tomatoes, walnuts, and lemon juice and toss.
Finally, season to taste and serve with generous drizzles of olive oil and freshly grated pecorino cheese.