Prep Watermelon: Trim off rind. Cut flesh into 1-inch cubes (or scoop balls). Remove seeds if needed.
Flash Freeze: Line a baking sheet with parchment paper. Spread cubes in a single layer, not touching. Freeze 2–3 hours until solid.
Store: Transfer frozen cubes into freezer bags or airtight containers. Press out excess air, label with date, and return to freezer.