Add the cubed watermelon and fresh lime juice into a blender. Blend until completely smooth so there are no chunks left, creating a juicy base for the slush.

Add ice cubes gradually and continue blending until the mixture becomes thick and frosty. Adjust the amount of ice depending on how slushy you want the texture.

Add fresh mint leaves and optional sweetener, then blend briefly just until combined. Avoid over-blending the mint to maintain a fresh, clean flavor.

Taste and adjust sweetness or lime if needed. Pour into chilled glasses and serve immediately while icy and refreshing.