Preheat oven to 350°F. Grease and flour a bundt pan then set aside.
Combine 1/2 cup sugar, 2 tablespoons cocoa, 1 tablespoon cinnamon in a small bowl. Set aside.
Cream together 1 cup softened butter, 3/4 cup plus 2 tablespoons sugar, and 3 eggs in an electric mixer. Blend in sour cream.
In a separate bowl, whisk together flour, baking powder, and baking soda. Slowly add to mixer. Stir in grated orange peel.
Pour about 1/3 of the batter into the pan. Sprinkle half the cinnamon sugar mixture over the batter. Cover with another 1/3 batter, sprinkle with remaining sugar, then top with the rest of the batter. Use a knife to cut through batter to marble/swirl together gently.
Bake for 50-60 minutes, then let cool for 10 before turning out of the pan onto a wire cooling rack. Let cool completely while making the glaze.
With an electric mixer, beat cream cheese until smooth. Add powdered sugar and beat until combined, then add orange juice and milk until you reach the desired consistency. It should be smooth and pourable but not too thin so it can set.
Pour glaze over cooled cake and top with orange zest as a garnish. Slice and serve!