Finely slice the spring onions and put to one side. In a large frying pan (skillet), cook the bacon for about 8-10 minutes over medium heat until the fat is rendered and the bacon is crisp. Remove from the pan, drain on a paper-towel-lined plate and cut the rashers in two crosswise.
In the same pan, increase the heat a little and cook the scallops in the bacon fat. Cook for two minutes, and then flip. Once flipped, add a small knob of butter to the pan and add the scallions. Cook for a further one to two minutes until the scallops are cooked through but still tender.
Build each sandwich with a layer of bacon pieces, the warm scallops, a sprinkle of spring onions and some of the salty juices from the pan. Serve immediately.