1. Preheat oven to 350°F. Toast walnuts on baking sheet 10 minutes. Cool, and coarsely chop.
2. Whisk together cheese, oil, lemon juice, lemon zest, garlic, and pepper in large bowl.
3. Cook pasta according to package directions. Drain, and reserve 1/2 cup pasta cooking water. Add drained pasta to cheese mixture, and toss to combine, adding some pasta water if mixture seems too thick. Stir in parsley and walnuts, and season with salt and more pepper, if desired.