Preheat the oven to 350 degrees F (175 degrees C). Spray the bottom and sides of a 9x13-inch baking pan with cooking spray.
Mix cookie mix, butter, and egg together in a large bowl until well blended. Stir in chopped candy bars. Press dough into the bottom of the prepared pan.
Bake in the preheated oven until light golden brown, 15 to 18 minutes. Let crust cool completely, about 1 hour.
Combine whipped topping and frosting in a large bowl until well blended. Reserve 1/4 cup chopped cookies; gently stir remaining cookies into frosting mixture until well combined. Spread over the cooled crust. Cover with plastic wrap and refrigerate until chilled, about 2 hours. Cut into 6 rows and 6 columns for 36 bars.