Preheat oven to 325 degrees. Brush a 6-cup Bundt pan (surlatable.com) with butter, and dust with flour, tapping out excess. Whisk together flour, baking powder, spices, and 1 teaspoon salt.
Grate zucchini on the large holes of a box grater, then squeeze dry in a clean kitchen towel or press in a ricer. (You will need 2 1/2 cups.)
Stir together eggs and sugar, then stir in melted butter, zucchini, and orange zest and juice. Stir in flour mixture. Transfer batter to pan.
Bake until a toothpick inserted into the center comes out clean, about 1 hour (cake will rise quite a bit over the top of the pan but should not run over). Transfer pan to a wire rack, and let cake cool for 10 minutes. Run a paring knife around edges of cake to loosen, and turn out onto wire rack. Let cool for at least 30 minutes.
Brush several layers of orange glaze evenly over cake, and garnish with candied zucchini before serving.
Unglazed cake can be stored at room temperature, wrapped in plastic wrap, for up to 1 day, or frozen for up to 1 month.