Grate zucchini and then squeeze dry in a kitchen towel to remove excess water. Measure out three cups.
Grease a 6-cup bundt pan and lightly flour. (Make sure to tap out excess flour.)
Whisk together flour, baking powder, and cinnamon. Set aside.
Stir together eggs and sugar. Gradually mix in melted butter, zucchini, orange zest and juice.
Stir in flour mixture just until combined. Pour into prepared pan.
Bake 55-65 minutes or until a toothpick inserted into the cake comes out clean.
Let cake cool on a wire rack for 10-15 minutes before inverting the cake pan and turning it out onto a wire rack. Let cool for an additional 30 minutes before glazing.
Orange Glaze
Whisk glaze ingredients together and drizzle over slightly cooled cake. If glaze is too thick, add more orange juice. If it is too thin, whisk in more sugar.