Preheat the oven to 325°F. Grease a 9-inch springform pan.
In a medium bowl, combine graham cracker crumbs, cocoa powder, granulated sugar, and melted butter. Mix until well combined. Press the mixture firmly into the bottom of the prepared springform pan to form the crust.
In a large mixing bowl, beat the softened cream cheese with an electric mixer until smooth and creamy. Gradually add the powdered sugar and vanilla extract, mixing until well incorporated.
Add the sour cream, eggs, orange zest, and orange juice to the cream cheese mixture. Beat on low speed until just combined, being careful not to overmix. Fold in the melted chocolate until evenly distributed.
Pour the cheesecake batter over the crust in the springform pan. Bake in the preheated oven for 50-60 minutes, or until the center is set but slightly jiggly.
Turn off the oven and crack the door open, allowing the cheesecake to cool in the oven for about 1 hour.
Remove the cheesecake from the oven and let it cool to room temperature. Cover and refrigerate for at least 4 hours, or overnight for best results.
To serve, carefully remove the sides of the springform pan. Slice and enjoy!