01 - Bring a large pot of salted water to a rolling boil. Add spaghetti and cook according to package instructions until al dente. Reserve 1/2 cup pasta cooking water, then drain spaghetti.
02 - While pasta cooks, heat olive oil in a large skillet over medium-low heat. Add sliced garlic and red chili flakes, gently sauté until garlic is fragrant and lightly golden, being careful not to burn.
03 - Add drained spaghetti to the skillet. Toss well to coat with garlic oil. If necessary, add some reserved pasta water to create a silky sauce. Fold in chopped parsley.
04 - Season with salt and freshly ground black pepper to taste. Transfer to serving plates and garnish with additional parsley if desired.