Start by caramelizing the onions. Slice the onion into thin rings and cut them in half. Heat the oil in a frying pan and add the onions. Sprinkle with a large pinch of salt and cook over a medium/low heat for 15-20 minutes until softened.
Stir in the soft light brown sugar and balsamic vinegar and continue cooking for a further 10 minutes.
Spread an even base of pesto onto the flatbread and arrange on top the feta and the caramelized onions. Cook in a preheated oven at 200ºC for 10-15 minutes.
