Measure out and combine the garlic, walnuts, arugula and parsley in a food processor and chop thoroughly.
Add olive oil to process even more until it resembles a pesto.
In a large bowl, mix the greens just processed with the cheese, vinegar, lemon zest and juice until just combined. Add salt and pepper to taste.
Prepare fresh fettuccine noodles and reserve at least a cup of pasta water.
Once noodles have cooked, drain. In the hot pot, return cooked noodles one serving at a time and mix with a dollop of the pesto. Add the pasta water to thin pesto as needed.Serve immediately with more grated Pecorino romano and cracked pepper.
Notes
Consider adding additional vinegar if you feel the flavor needs a little more pop. I tried adding a splash of lemon juice and a dash of the vinegar on two different occasions. I think the vinegar is what really makes this dish a winner.