Heat a large pot of salted water to boiling for the pasta.
Heat the olive oil in a large sauté pan or skillet over high heat. Add the greens and cook, stirring constantly, until wilted. Add the cream, goat cheese, and walnuts. Reduce heat and cook, stirring constantly, until the cheese melts. Season with pepper to taste. Add the citrus zest or tomatoes if using and heat through, although it’s perfectly delicious as is.
Add the pasta to the boiling water and cook until tender, about 2 minutes if the pasta is thin. Drain and transfer to a pasta bowl. Add the sauce to the pasta and quickly toss to combine. Serve hot.