1. To prepare cake: Preheat oven to 350 degrees F. Coat a 9-by-13-inch baking dish with cooking spray.
2. Toast walnuts in a small baking pan in the oven until fragrant, 5 to 10 minutes.
3. Whisk flour, baking soda, salt and cinnamon in a medium bowl. Whisk eggs, sugar, buttermilk, oil, vanilla and 1/4 cup of the reserved pineapple juice in a large bowl until blended. Stir in pineapple, carrots and coconut. Add the dry ingredients and mix with a rubber spatula just until blended. Stir in the nuts. Scrape the batter into the prepared pan, spreading evenly.
4. Bake the cake until the top springs back when touched lightly and a toothpick inserted in the center comes out clean, 40 to 45 minutes. Let cool completely on a wire rack.
5. To prepare frosting and finish cake: Place coconut in a small baking pan and toast in the oven at 300 degrees F, stirring several times, until light golden, 5 to 10 minutes.
6. Beat cream cheese, confectioners' sugar and vanilla in a mixing bowl with an electric mixer until smooth and creamy. Spread the frosting over the cooled cake. Sprinkle with the coconut.

Yield: 16 servings