Mussels puttanesca with linguine

Name: Mussels puttanesca with linguine
Ingredients: 2 tbsp olive oil; 1 small onion, finely chopped; 2 garlic cloves (if using mussels in garlic, omit this extra garlic if you like), finely sliced; large pinch dried red chilli flakes; 1 x 400g tin chopped tomatoes; 4 anchovy fillets; 70g/2½oz black olives, stones removed; 2 tbsp capers; 100ml/3½fl oz dry white wine (if not using mussels in wine); 150g/5½oz linguine (or spaghetti/fettucine); 2 x 250g pouches vacuum-packed cooked mussels (in garlic or white wine is fine); few sprigs fresh parsley, stalks removed and leaves finely chopped; salt