Freeze your Watermelon: Cube your watermelon, and freeze the amount you'll need on a baking sheet. This ensures that you won't end up with individually frozen pieces, rather than a giant frozen ice block of watermelon. Once the watermelon is frozen on the baking sheet, you can transfer it to a freezer bag or container and keep frozen until ready to use.
Make the Margaritas: Add all liquid ingredients to your Oster ActiFit Smoothie Blender first. Then, add the frozen watermelon. Twist the cup to blend until smooth and creamy.
Serve: Snap on the spill proof lid that comes with the blender cup, or run a lime wedge run around the rim of a glass and dip in salt. Pour into the glass and enjoy immediately!