Cut the seedless watermelon into roughly 1-inch cubes and place them in a large blender.

Add the granulated sugar, fresh lime juice, and a pinch of salt to the blender. Blend on high speed until completely smooth.

Strain the mixture through a fine-mesh sieve into a shallow freezer-safe dish to remove pulp.

Freeze for about 30-45 minutes until ice crystals form around the edges.

Scrape the icy edges towards the center with a fork and return to the freezer. Repeat every 30-60 minutes for about 3-4 hours until fully frozen.

Scoop the granita into chilled bowls or glasses and garnish with mint or lime if desired.