Preheat your oven to 350°F (175°C). Grease your bundt cake pan thoroughly with butter or a nonstick spray, then dust lightly with flour to ensure the cake releases easily after baking.
In a large bowl, sift together 2 cups of all-purpose flour, 1 1/2 cups of granulated sugar, 1 cup of unsweetened cocoa powder, 1 teaspoon of baking powder, 1 teaspoon of baking soda, and 1/2 teaspoon of salt. Stir in 1 tablespoon of freshly grated orange zest.
In a separate bowl, whisk together 1 cup of buttermilk, 1/2 cup of vegetable oil, 3 large eggs, and 1 teaspoon of vanilla extract until smooth and fully combined.
Pour the wet ingredients into the dry ingredients and gently fold the mixture together with a spatula until just combined. Avoid overmixing to keep your cake tender.
Carefully stir in 1 cup of boiling water. The batter will be thin—this is normal and helps keep the cake moist. Then fold in 1/2 cup of chocolate chips.
Pour the batter evenly into your prepared bundt pan. Bake for 50-60 minutes or until a toothpick inserted near the center comes out clean or with just a few moist crumbs. Avoid opening the oven door too frequently.
Let the cake cool in the pan for about 15-20 minutes before gently inverting it onto a wire rack to cool completely. If desired, drizzle with chocolate glaze and garnish with fresh orange slices.