Preheat the oven to 325°F. Grease and flour a 10- to 12-cup Bundt pan. (I use vegetable shortening.) Combine the flour, baking powder, baking soda, cinnamon, ginger, nutmeg, and salt in a large bowl.
Beat the butter and sugars in a stand mixer fitted with the paddle attachment until light and fluffy. Add the eggs, one at a time, beating just until the yellow disappears after each addition. Beat in the vanilla.
Add the flour mixture alternately with the buttermilk in three additions, beginning and ending with the flour mixture. (Scrape down the sides of the bowl if needed to ensure the batter is well mixed.)
Fold in the carrots, pecans, and pineapple. Spread the carrot cake batter into the prepared pan and bang the pan on the counter to remove any air bubbles. Bake for 1 hour or until a toothpick inserted in the center comes out clean.
Remove the cake from the oven and cool in the pan for 10 minutes. Run a sharp knife around the edges and turn out the cake onto a cooling rack to cool completely.
While the cake cools, make the glaze. Beat the cream cheese in a medium bowl with an electric mixer until smooth. Add the powdered sugar, orange zest, orange juice, vanilla, and salt and beat until creamy.
Place the cake on a cake plate or cake stand. Spoon the glaze on top of the cake. Garnish with orange zest curls and candied orange slices if desired.