Heat oil in a large non-stick frying pan over medium-high heat. Add onions. Cook, stirring, for 5 minutes or until soft and light golden.
Add garlic and tomatoes. Cook, stirring, for a further 2 minutes or until tomatoes have softened slightly. Stir in vinegar. Bring to the boil. Remove from heat. Cool slightly.
Place breads on baking trays and spread with tomato paste. Top evenly with tomato and onion mixture, chicken and bocconcini. Season with freshly ground pepper.
Bake in a preheated 220°C oven (fan-forced) for 10-12 minutes, until bread is crisp and topping is lightly browned.
Scatter basil over pizzas to serve.

Check labels on Lebanese bread and choose the brand lowest in sodium.
Shredded, cooked, skinless chicken breast is available from the deli counter in supermarkets. Alternatively, substitute leftover skinless, roast chicken.