Preheat oven to 350 and grease cake pan (6 mini-bundts of about 4" diameter, or a 9x13"). Combine sugar, oil, and vanilla; add eggs one at a time, beating thoroughly after each addition.
Combine dry ingredients in separate bowl and stir into wet ingredients just enough to combine. Stir in carrots, drained pineapple, and walnuts.
Pour into prepared pan and bake 22-25 minutes for bundts, 45 minutes for 9x13", or until a knife point comes out clean.
Whip softened cream cheese, butter, and orange zest together until well combined. Add confectioners sugar until desired consistency reached -- will be between 1-3/4 and 2 cups.
Cool cakes thoroughly before frosting. To remove from pan, allow to cool in pan for about 10 minutes. Thump pan firmly on hard surface, then invert. Allow to cool thoroughly.