Chop the watermelon into chunks and freeze overnight until solid.
Fit your Nama J2 juicer with the sorbet attachment.
Feed the frozen watermelon through the juicer, adding the lime zest and juice as you go.
Once fully processed, stir in the maple syrup if using, and add a small pinch of salt.
Serve immediately for a soft sorbet, or transfer to a container and freeze for 1–2 hours for a firmer texture.