Add the all purpose flour, cocoa powder, kosher salt, baking soda, and cinnamon to a bowl. Mix with a whisk until the ingredients are evenly distributed.
In the bowl of a stand mixer fitted with the paddle attachment, add in the melted butter, brown sugar, and granulated sugar. Mix on medium speed for about 1 minute until the mixture slightly lightens in color. While mixing on medium low speed, add in the eggs one at a time, making sure it's been fully incorporated before adding in the next. Then mix in the vanilla extract.
Add in the bowl of dry ingredients. Mix on low speed until just combined. Then mix in 3/4 cup of the KitKats, 3/4 cup of the Hershey's Cookies n' Creme, and 3/4 cup of the Oreos until the chocolates are evenly distributed throughout the dough. Remove the bowl from the stand mixer. Cover the bowl with plastic wrap and refrigerate for 1 hour.
Preheat the oven to 375˚F. Line a few baking sheets with parchment paper. set aside.
Scoop balls about 2 1/2 tablespoons in size. Roll them into uniform sized balls and place them onto the parchment lined baking sheet, spacing them 2 1/2 inches apart from each other. Use the remaining KitKats, Hershey's Cookies n' Creme, and Oreos to top each cookie dough ball.
Bake the cookies in the oven for 12-13 minutes until the edges are golden brown and set but the center is still soft. When you remove the cookies from the oven, firmly tap the bottom of the baking sheet onto the surface so that the cookies crinkle and flatten. If your cookies spread into weird shapes, immediately use a rubber spatula to push in the edges of the cookies until it forms a circle. Sprinkle flakey salt on top. Allow the cookies to cool on the baking sheet for a few minutes before transferring to a wire rack to cool completely. Enjoy!