Place a layer of sliced onions in an oiled baking dish, cover onions with a layer of apple rings, which should be cored but not peeled. Mix together the sugar, nutmeg, thyme and lemon rind, and sprinkle over the apples. Repeat the process until onions and apples are used up. Pour over the top the lemon juice and melted butter or margarine. Bake for 1 hour at 350 degrees F. Makes 4 servings.