01 - Bring a large pot of salted water to a boil. Cook spaghetti until al dente according to package instructions. Reserve 1/2 cup pasta water and drain the pasta.
02 - Heat olive oil in a large skillet over medium heat. Add sliced garlic and sauté, stirring frequently, until golden and fragrant, about 2 minutes. Avoid burning the garlic.
03 - Stir in red pepper flakes if using and cook for 30 seconds to release flavor.
04 - Add cooked pasta to skillet along with half of the reserved pasta water. Toss to coat evenly, adding more pasta water as needed to create a silky sauce.
05 - Remove pan from heat. Stir in chopped parsley, season with salt and black pepper to taste.
06 - Serve immediately, optionally topped with Parmesan cheese and lemon zest.