Step 1: finely chop the onion and mix into the mince with the egg.
Step 2: divide into portions and pat into rounds on a floured board.
Step 3: put a cheese triangle into the middle of each one and carefully mould mince round the cheese so its completely surrounded.
Step 4: put into fridge while you preheat oven 200c for 10 mins.
Step 5: put burgers onto an oven tray and cook for 20-25 mins.
Step 6: this might be longer depending on how thick you made your burgers!