Spray a 9×13″ baking dish with nonstick spray then set aside.

Roughly chop 16 cookies then add to a very large bowl with the Chex and set aside. Chop remaining 4 cookies a little more fine then set aside.

Add butter to a microwave-safe bowl then microwave for 30 seconds or until melted. Add marshmallows then stir to coat and microwave for 1 minute and 20 seconds. Stir until smooth then immediately pour over Chex mixture and mix until evenly coated. Scoop into prepared baking dish then press into an even layer (I sprayed the bottom of large measuring cup with nonstick spray then used that to press.)

Add chocolate chips to a small microwave-safe bowl then microwave in 30 second intervals, stirring between each interval, until melted and smooth. Drizzle over the top of the bars then sprinkle on remaining cookies. Let cool completely before cutting into bars.