Heat the oil in a small frypan pan and cook the onion for about 5 minutes until soft. Remove from the pan, drain off any oil on some kitchen roll then allow onion to cool.
Mix together the mince, garlic, cumin, coriander, tomato puree, chilli sauce, mustard, Worcestershire sauce, mixed herbs, egg and crushed chilli flakes in a bowl. Stir in the onions and sprinkle over some salt and pepper.
Shape the mixture into eight burgers and chill for 10 minutes. Fry, grill or barbecue the burgers for roughly 5 minutes each side, depending on taste.