Remove the rind from a seedless watermelon and slice into chunks. Freeze the chunks in several freezer bags for a least 24 hours.
When ready to make, let the frozen watermelon sit at room temperature for about 20 minutes to soften slightly. This makes a big difference!
Add the slightly defrosted watermelon chunks and lime juice to a blender. Blend until a smooth consistency.
Pour into a bowl and garnish with fresh mint leaves if desired.