In a large skillet over medium low heat, cook the garlic in olive oil until golden. Remove garlic from the pan. Add the walnuts and cook, stirring until lightly toasted, about 5 minutes.
Meanwhile, bring a large pot of water to a boil. Add salt and the pasta. Cook, stirring frequently, until the vermicelli is al dente, tender yet firm to the bite.
Drain the vermicelli, reserving half cup of the cooking water. In a large serving bowl, toss the vermicelli with the nuts and just enough cooking water to keep it moist. Add the parsley, if using, and sprinkle generously with pepper.
Add cheese and toss again. Serve immediately.