Heat oven to 350 degrees F. Lightly coat 13 x 9 x 2-inch baking pan with cooking spray.
Beat flour, sugar, eggs, baking soda and pineapple with its juice in large bowl on low speed until well blended, about 1 minute. Pour into prepared baking pan.
Bake in 350 degree F oven 30 to 35 minutes, until golden. Cool on rack.
Combine milk, sugar and margarine in medium-size saucepan. Boil for 2 minutes or until consistency of thick soup. Remove from heat. Stir in coconut, pecans and vanilla. Let cool. Pour over cake. Makes 24 servings.