Preheat oven to 350 degrees F. Place cupcake liners into standard muffin tin.
Prepare brownie mix according to package directions.
Take 1 cookie dough piece from the pack and roll it into a ball. (About 1 tablespoon.) Place one cookie dough ball in the bottom of each muffin tin cup.
Add 2 tablespoons of brownie batter on top of the cookie dough.
Bake for 20 to 25 minutes until a toothpick inserted into the center comes out clean.
Remove cupcakes from pan and allow to cool completely on a wire rack.
While cupcakes cool, Place 12 Oreo cookies into a ziploc bag and seal closed. Use a rolling pin to crush the cookies. Add cookie crumbs to buttercream and mix until completely incorporated.
Pipe frosting onto cupcakes using a piping bag and wide tip or a ziploc bag with a corner cut off. (If using a piping bag and tip make sure that your Oreo pieces are small enough to pass through easily.)
Garnish each cupcake with an Oreo stuck into the frosting.