Measure and chop the watermelon into small chunks, about 1-inch pieces, ensuring they are free of seeds and rind.
Add the watermelon chunks, salt, and lime juice to a high-speed blender.
Blend on high until the mixture is completely smooth and uniform, approximately 30 seconds. Stop and scrape down sides as needed.
Pour the blended mixture into a shallow, freezer-safe container, spreading into an even layer.
Place the container in the freezer. Every 30 minutes, use a fork to scrape and mix the mixture to prevent large ice crystals, repeating 3-4 times over a total freezing period of about 3-4 hours.
Once the sorbet has a firm, scoopable texture, serve immediately in bowls, garnished if desired with lime zest or mint.