In a large bowl mix chocolate cake mix and 6 oz of Dr pepper. Stir until well combined and the consistency of cookie dough. If necessary add a little more Dr Pepper. Stir in 1 cup of chopped pecans (optional).
Scoop into tablespoonfuls onto parchment lined baking sheet and bake for 10 minutes.
Remove and allow to cool.
Glaze
Whisk together powdered sugar and Dr Pepper until you achieve your desired glaze consistency.
Drizzle over cooled cookies.
Notes
Yes, you can use Diet Dr pepper. I am sure this works with other sodas, but I haven't tried.
Gluten Free
You can use a gluten free cake mix for these cookies. HOWEVER, gluten free cake mixes tend to be smaller than regular ones. Start out with only 3 oz of Dr. Pepper until you get the desired cookie dough consistency.