Peel and chop the onions based on your preference.
You can chop multiple onions.
Then store the chopped onions in a freezer safe container or freezer bag.
Store the bag or container in the freezer for up to 3 months.
When you need some onions, break apart the frozen chopped onions and take what you need for your recipe.
Video
Notes
You can also flash freeze the onions by placing the onions on a baking sheet, freeze for 1 hour and then place in a storage bag or container. Flash freezing the onions make them easier to remove from the container when they are needed.