I originally had a version of this sandwich at a small little restaurant in MN on a business trip. They were nice enough to give me the recipe for their marinade and the rest was simple to figure out - and you can't believe what they charged for it. It is very quick and easy to make, especially on the grill for a perfect summertime light and healthy meal. A bit of a kick from from the wasabi and the cool flavors from the cucumber and onions are perfect with the Asian marinated salmon. Make sure to use a good roll, either a ciabatta or baguette are perfect for this sandwich. Serve with a light citrus salad or an Asian coleslaw.