Grease an 8-inch (20-cm) fluted oval or round cake pan.
Preheat oven to 325°F (165°C).
Cut prunes and apricots into small pieces; mix with raisins and walnuts in a small bowl.
Cream margarine, granulated sugar, salt, lemon peel and vanilla in a large bowl until light and fluffy.
Beat in eggs one at a time, adding a tablespoon of flour with each egg after the first.
Sift remaining flour with baking powder; fold into egg mixture with dried fruit mixture.
Turn batter into greased cake pan; smooth the surface.
Bake 1-1/2 to 1-3/4 hours or until a skewer inserted in center comes out clean.
Turn out cake onto a rack to cool.
Sift powdered sugar over cooled cake.