Bring a large pot of salted water to a boil.
Add the capellini noodles and cook for 2–4 minutes until al dente.
Reserve ¼ cup pasta water, then drain the noodles.
Heat olive oil in a skillet over medium heat and sauté the garlic for about 30 seconds.
Add the lemon juice and optional lemon zest.
Toss the cooked capellini into the skillet and mix gently.
Add a splash of reserved pasta water if needed for a silky sauce.
Stir in parsley and season with salt and black pepper.
Top with Parmesan cheese if desired and serve immediately.