Slice the cucumber as thinly as you can, sprinkle with a little salt, and let it sit for about 10 minutes to draw out excess moisture.
Tear or cut the crab stick into bite-sized pieces.
In a bowl, combine the Greek yogurt, crab stick, boiled egg, olive oil, whole grain mustard, oligosaccharide syrup, and pepper, and mix well.
Squeeze the salted cucumber firmly to remove as much liquid as possible, then fold it into the bowl with the rest of the mixture.
Tip.Removing enough moisture from the cucumber keeps the sandwich from turning soggy and makes the flavor much more concentrated.
Pile the mixture generously onto lightly toasted bread, and it's ready to serve.