Preheat oven to 350°F. Grease or line an 8"x8" baking pan with parchment paper, leaving an overhang for easy removal.
In a medium bowl, sift together cocoa powder, flour, and baking powder.
In a large bowl, whisk together the melted and slightly cooled butter and granulated sugar until well combined.
Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
Gradually add the dry ingredients to the wet ingredients, stirring until just combined.
Gently fold in chocolate chips.
In a mixing bowl, beat the softened cream cheese and granulated sugar until smooth and creamy. Add the egg and vanilla extract, and beat until well combined.
Spread the brownie batter evenly into the prepared baking pan.
Sprinkle half of the chopped Oreos over the brownie batter.
Pour the cheesecake batter over the brownie layer in the baking pan, spreading it evenly.
Sprinkle the remaining chopped Oreo cookies over the cheesecake layer, pressing them gently into the batter.
Bake 35-40 minutes, or until the edges are set and the center is slightly jiggly.
Remove from the oven and let the Cheesecake Oreo Brownies cool completely in the pan on a wire rack.
Once cooled, refrigerate the brownies for at least 2 hours (or overnight) to set.
Once chilled, use the parchment paper overhang to lift the brownies out of the pan. Cut into squares and serve.