When the melon cubes are frozen take them out from freezer. Put them in a blender jar. ( make sure that blades of the jar are strong enough to blend frozen melon cubes). Add lemon juice, sugar, lemon zest, and salt. First use pulse button of your mixer to break melon cubes. If required add some water. If the cubes are not very tough, they break easily and you will not need to add water. Blend the mixture till you get soft gooey pulp. Pour the pulp in an airtight container and keep it in freezer for four hours. Melon sorbet is ready. Scoop out required amount and serve in ice cream cup / bowl.