To mince green onion, first remove any outer parts that are wilted. Cut off tips and root. With a rocking motion of your chef's knife finely chop green onion going down the stalk. For finely minced, continue to chop using rocking motion until it is the desired size. Green onion and scallion can be interchangeable in recipes, so don't worry if recipe calls for scallion and the store only has green onions.