Place the lemon slices in a heavy kettle and add 2 cups water.
Bring to a boil and simmer for about 50 minutes or until the rind is soft.
Peel, core, and chop the tomatoes and apples, then add with sugar and salt to the lemons.
Heat, stirring often, until the sugar dissolves.
Cook, stirring and skimming, for 45 minutes.
Add the walnuts, raisins and ginger to the cooked mixture.
Cook, stirring several times, for about 15 minutes or until the syrup is thick and the fruit is clear.
Pour in hot sterilized glasses and seal.