Bring a large pan of well-salted water to the boil and cook the spaghetti for about 10 mins, or until al dente – it should retain a little bite.
When the pasta is nearly ready, heat the oil in a frying pan set over a medium heat and sizzle the garlic and chilli, if using, for 1 minute until fragrant and the garlic is lightly golden but not brown (the garlic will taste bitter if it gets too dark).
Drain the spaghetti and add it to the garlicky oil with the parsley. Season and toss to combine, then serve.
