finely chop the onion and mix into the mince with the egg.
divide into portions and pat into rounds on a floured board.
put a cheese triangle into the middle of each one and carefully mould mince round the cheese so its completely surrounded.
put into fridge while you preheat oven 200c for 10 mins.
put burgers onto an oven tray and cook for 20-25 mins.
this might be longer depending on how thick you made your burgers!