Cook spaghetti according to package directions. Reserve 1 cup pasta water before draining.
Meanwhile, heat oil in a large skillet over medium-low heat. Cook garlic and pepper flakes slowly 4-5 minutes, stirring often, 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.