Peel the onions, halve and slice thinly.
Cut the Quorn Roast Beef Style slices into quarters and then each quarter in half to give you 48 little triangles.
Heat the oil in a large, heavy-bottomed frying pan. Add the onions and a pinch of salt and cook on low to medium heat, stirring gently occasionally. If the onions stick, add a splash of water to deglaze the pan. Do allow the onions to brown gently.
Keep stirring occasionally until the onions are very soft and gently browned.
After about 20 minutes of cooking add the sugar and balsamic vinegar and cook for a further 10 minutes. Allow to cool.
Toast the mini pittas in a medium oven for about 5 minutes (or according to packet instructions) until puffed. Split each one open.
Stuff each pitta with 3 triangles of Quorn Roast Beef style slices, a slice of tomato, a slice of cucumber, a spoonful of caramelised onion and mustard to taste.
Serve and Enjoy!