Liz McClarnon's tuna, red pepper and olive tart

Preheat oven to 200°C/gas mark 6. Cut the pastry into 4 discs approximately 10cm/4" wide. Heat the olive oil in a large frying pan, add the onions and cook over a low heat for 10-12 mins or until soft and golden. Add the vinegar and cook for 2 more mins, then allow to cool. Put the pastry discs onto a non-stick baking tray. Divide the onion mixture between each, leaving a 1cm border to allow the pastry to puff up. Bake in the oven for 10-12 mins or until puffed up and golden brown. Mix the black olives, rocket, red peppers and tuna together and season lightly. Once the discs of pastry come from the oven, spoon the tuna mixture on top and serve straight away.