Place the cubed watermelon into a blender or food processor and blend until completely smooth.

Taste the blended watermelon and, if desired, add granulated sugar to enhance sweetness. Blend again to incorporate the sugar.

Add 1 tablespoon of lemon juice to balance the flavor and blend once more.

Pour the watermelon mixture into the Ninja Creami pint container, ensuring the mixture does not exceed the max fill line.

Cover the container with the lid and freeze upright for at least 24 hours to allow it to solidify properly.

Once frozen, remove the container from the freezer and place it into the Ninja Creami machine following the manufacturer's instructions.

Select the 'Sorbet' setting on the Ninja Creami and let the machine process the frozen mixture into a smooth sorbet.

If the sorbet is too crumbly after the first cycle, use the 'Re-spin' function to achieve a creamier texture.

Serve immediately or store in the freezer in an airtight container for later enjoyment.