To make the burgers, place the minced beef 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. Alternatively, use a large frying pan. If using a frying 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 more well done. Remove and leave to rest for a few minutes. Meanwhile, 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 and onion rings. Top each one with a burger and put on warmed plates. Add a serving of the onion marmalade to each one, then place the top half of the bun on top to serve.