In a frying pan over low heat, saute the garlic in the olive oil until golden but not browned. Add the chillies and the reserved cooking liquid. Add the spaghetti and season with the chopped parsley, salt and pepper. Toss so that the spaghetti is coated in the olive oil mixture and everything is well combined. Serve immediately with grated Parmesan or Pecorino Romano, if desired.