In Japanese, this style of cutting up long onions is called "white-hair slicing", in the image of slicing up the onion into such fine strips that these are similar to white (gray) hair.
Chop up into 4 cm (1.6 in.) lengths, slice each vertically and remove the soft core. Stack the outer layers and starting at one edge, julienne across into ultra-fine strips. These ultra-fine strips are not cooked when used as garnish. If placed in water for about 10 minutes, drained and squeezed of any excess moisture, these strips will be fresh and crunchy yet mellow in flavor.