01 - Add the frozen watermelon cubes, coconut milk, lime juice, and agave syrup (or honey) to a high-speed blender.
02 - Blend on high until smooth and slushy, scraping down the sides if necessary.
03 - Taste and adjust sweetness, adding more agave or honey if desired.
04 - Pour into chilled glasses. Garnish with lime slices and fresh mint leaves if desired. Serve immediately.