Preheat the oven to 350°F. Line a 9 x 9 inch pan with foil and spray the foil with cooking oil.
In a large enough microwavable bowl, melt the chocolate and butter until the butter has melted, 1 to 2 minutes. Remove the bowl from the microwave and continue to stir until chocolate is completely melted.
Stir in the sugar. Using a kitchen mixer, beat in the eggs and vanilla. Mix in the flour and stir in half of the chopped Oreo cookies.
Pour the batter into the prepared pan and top with the remaining chopped Oreo cookies. Bake for 30 to 35 minutes until a toothpick inserted in the center comes out clean.
Allow the brownies to cool completely. Then use the foil to lift the brownies from the pan. Cut into squares.