Preheat oven to 350 degrees and spray a 9 X 13" pan with cooking spray or line it with parchment
In a bowl, mix together flour, baking powder, baking soda, cinnamon and salt; set aside.
In another bowl, beat sugar and oil; add eggs and beat until light.
Add in dry ingredients and stir; fold in carrots and pineapple.
Pour into your prepared pan and bake at 350 for 40 - 50 minutes for a 9X13" pan
Cool and cut into 12 squares.
For the icing, in the bowl of an electric mixer, combine all ingredients and beat until smooth.
Cut each cake square horizontally and fill with frosting
Replace with top cake and wrap individually in plastic wrap. Freeze them and take them out, one at the time, for fresh carrot cake at any time.
NOTE: If you have leftover icing, freeze it in an air-tight container.
Notes:
If you'd like to make these into Twinkies (you can find Twinkie pans online) or cupcakes and bake for 20-25 min. Pipe the frosting into the bottom of the Twinkies or cupcakes to make it seem as though it is in the middle