Bring a pot of water to a boil, then blanch the mung bean sprouts by adding them to the water and leaving them for a minute or two, until they begin to soften. Immediately drain them but DO NOT RINSE! (this causes them to retain more moisture, weighing down the shoots and making them soggy.) Let them to cool in the colander, occasionally giving them a toss.
While they cool, slice the green onion on the bias into pieces about 2-3mm thick. Add these to the blanched bean sprouts, along with the garlic, salt, sesame seeds and sesame oil, then lightly toss until they are evenly coated.
Once completely cooled, store in an airtight container.