Heat oven to 350°F (or 325°F for dark or nonstick pan). Spray bottom and sides of 13x9-inch pan with baking spray with flour.
In large bowl, stir cake mix and flour. Reserve 1/3 cup cake mix mixture. To remaining mixture, add water, oil, eggs, cinnamon and nutmeg; beat with electric mixer on low speed 30 seconds, then on medium speed 2 minutes, scraping bowl occasionally. In medium bowl, stir carrots, raisins, walnuts and reserved cake mix mixture until coated. Stir into batter; pour into pan.
Bake 35 to 43 minutes or until toothpick inserted in center comes out clean. Cool completely, about 2 hours.
In large bowl, beat powdered sugar, cream cheese, butter and vanilla on low speed until blended. Beat on medium speed until smooth and creamy. Spread frosting over cake. Sprinkle with coconut. Store covered in refrigerator.