Heat the oil in a large lidded pan, then add the onion and cook for 5 minutes. Add the garlic, olives and chilli, and cook for a further 5 minutes. Stir in the chopped tomatoes and cherry tomatoes and cook for 8 minutes.
Meanwhile, bring a pan of water to the boil, add the spaghetti and
Add the mussels to the pan with the tomatoes, discarding any open ones that don’t close when tapped, then cover with a lid and simmer for 2-3 minutes.
Stir in the cooked spaghetti and reserved cooking water along with the basil. Season and serve, discarding any mussels that have not opened.