Preheat oven to 350 degrees F. Line a 13×9 inch metal pan with foil and spray with cooking spray.
Mix the brownie mix, eggs, oil, and water together in a mixing bowl and beat for 50-60 strokes or until mixed.
Pour into pan and set timer for 25 minutes.While brownies cook, mix together the marshmallows, walnuts and a little less than a cup of the chocolate chips (you’ll be saving some for the end).Pull brownies from the oven after 25 minutes, quickly sprinkle with marshmallow mixture, then return to oven for 5 minutes so that marshmallows can melt**.
Remove from oven.
Sprinkle remaining chocolate chips over top of hot brownies and if you’d like, sprinkle on some more walnuts so that everything appears balanced.
Let cool at room temperature for about an hour.
Transfer to the refrigerator for another hour to set the chips.Lift the brownies from the pan and cut into 16 large squares.
