Preheat oven to 350 degrees F. Grease 15 1/2 x 10 1/2 x 1-inch rimmed baking sheet.
Stir first 8 ingredients in large bowl to blend. Use an electric mixer to beat in pumpkin, eggs and oil and beat until blended. Mix in raisins. Spread batter in prepared pan. Bake until toothpick inserted in center comes out clean (about 25 minutes). Cool in pan on rack.
Beat frosting ingredients in medium bowl until well mixed. Spread frosting over cake in thin layer. Cut cake into bars and serve.
SOURCE: RecipeGirl.com (Adapted from Bon Appetit )