Wash the green onions under running water, using your fingers to scrub off any dirt. Remove any wilted leaves and discard. Pat dry.
Trim the green onions then slice them into pieces.
Spread the slices out on a lined baking sheet. Place the sheet in the freezer, somewhere it won't get bumped, for about an hour or until frozen solid. Alternatively, you can skip this step but I like to flash freeze them so they don't clump together as much in the freezer.
Once frozen, transfer the slices to freezer-safe bags or containers. Remove as much air as possible, seal tightly, and label.
Store in the freezer for up to 3 to 4 months.
Notes
Use frozen green onions directly from frozen (do not thaw) in hot dishes. They should not be served in raw dishes, since they will get mushy.