Arrange watermelon cubes in a single layer on a parchment-lined baking sheet. Freeze for at least 2 hours or until completely solid. (This step is the key to a creamy, smooth texture — don't skip it.)

Once frozen, transfer the watermelon cubes to a high-powered blender or food processor. Add the fresh lime juice, granulated sugar, kosher salt, and lime zest if using.

Blend on high, stopping to scrape down the sides as needed, until the mixture is completely smooth and creamy. Taste and adjust sweetness by adding more sugar if needed, then blend again briefly to combine.

Pour the blended mixture into a freezer-safe container (a loaf pan works perfectly). Use a spatula to smooth the top.

Press a sheet of plastic wrap directly onto the surface of the sorbet to prevent ice crystals from forming. Cover with a lid or additional plastic wrap.

Freeze for at least 4 hours, or overnight, until firm enough to scoop.

When ready to serve, remove from the freezer and let sit at room temperature for 5-10 minutes to soften slightly. Scoop into bowls or cones and garnish with fresh mint, a lime wedge, or a small slice of watermelon.