Yes, after you've folded the Gyoza and placed them on a parchment-lined sheet pan, put the whole pan in the freezer until the dumplings are fully frozen. Then you can transfer the frozen potstickers to a freezer bag to store them. You can cook these frozen Gyoza in the same way you cook fresh ones; however, you will need to add a little more water and steam them for an additional 1-2 minutes.