To make the burgers, place the steak in a bowl with the onion, garlic, spring onions and egg. Mix until well combined and season to taste, then shape into 4 even-sized patties. Cover and chill until needed.
If using a charcoal barbecue, light it 30 minutes before you want to start cooking. If using a gas barbecue, light it 10 minutes beforehand. 3.
Alternatively, use a heavy bottom pan. If using a pan, place over a high heat until very hot. Sear the burgers for 2 minutes on each side, then cook for another 5 minutes on each side for medium-rare or longer if you prefer your burgers well done. Remove and leave to rest for a few minutes.
Lightly toast the cut sides of the ciabatta buns until lightly charred.
Smear the bottom of the ciabatta buns with mayonnaise, followed by the lettuce, a slice of Cheddar cheese. Top each one with a burger and put on warmed plates. Add a dollop of the onion marmalade to each one and place the top of the burger buns to the side to serve.