Place the apples or pears in a saucepan with the water, cinnamon, ginger, nutmeg and sultanas.
Stir over a medium-low heat, until the they have softened and almost formed a purée; this should take around about 10 minutes, depending on how ripe the fruit is. Add a little water during cooking if mixture looks too dry.
Place the yogurt in a bowl. Top with the stewed apple and sprinkle over the walnuts.