First, wash and chop your green onions. Then, place them in a freezer-safe container of a convenient size. I used some silicone cupcake molds (I hate baking in them, so I might as well use them for something, right?). Add enough water to each just to cover, and put them in the freezer until they're solid.
Take them out of the freezer and remove them from the cups (that's the nice thing about silicone - you can just flip it right out). Voila! Little green onion hockey pucks.
Put into a freezer container and freeze until ready to use. I've kept these for six months or more. You can use them as is in soups, stews, and other saucy things where a couple extra tablespoons of water won't matter, or you can thaw them out before you use them. They do get a little slimy so I wouldn't use them in a salad or anything, but they're good in just about any cooked dish. Enjoy!