Preheat the oven to 350 degrees F. Grease and flour a 13 X 9 X 2-inch baking pan. In a medium saucepan, bring the raisins and water to a boil and simmer for 1 minute.
Remove from the heat and cool slightly. Stir in the granulated sugar and oil. Add the egg. Combine the flour, cocoa, baking soda, salt and cinnamon, then stir the mixture into the raisin mixture, blending well.
Stir in the nuts. Pour the batter into the prepared pan and bake for 25 to 30 minutes or until a wooden pick inserted in the center comes out clean.
Place on a wire rack to cool in the pan. When cool, sprinkle with the confectioners'' sugar. If you like a design, use a paper table doily as a stencil when sprinkling the sugar over the cake.