Cook spaghetti according to package directions. Reserve 1 cup pasta water before draining.
While pasta cooks, heat olive oil in a large skillet over medium-low heat. Add garlic and red pepper flakes and cook slowly, stirring often, for 4-5 minutes until garlic is golden but not browned.
Add drained pasta directly to the skillet along with 1/2 cup pasta water. Toss vigorously over medium heat for 1-2 minutes until a light sauce forms.
Season with salt and pepper. Add more pasta water if needed.
Remove from heat, toss with Parmesan, and top with fresh parsley.