Combine flour, sugar, baking soda and cinnamon in a medium-sized bowl and stir to mix well. Stir in the pineapple, including the juice, and the milk, egg whites, and vanilla extract. Fold in the carrots, raisins, and if desired, the pecans.
Coat a 9 x 13-inch pan with nonstick cooking spray. Spread the batter evenly in the pan and bake at 325 for 35 minutes or just until a wooden toothpick inserted in the center of the cake comes out clean. Cool to room temperature.
To make the icing, combine all of the icing ingredients in a food processor and process until smooth. Spread the icing over the cake and serve immediately. Refrigerate any leftovers.