Line a 9-inch square baking pan with waxed paper, overlapping all 4 sides. Spray with cooking spray.
Place a nonstick pan over low heat and add the butter. When melted, add two-thirds of the marshmallows and cook, stirring, until the marshmallows have melted and combined with the butter, about 3 minutes. Next, fold in the chocolate chips and stir until they are melted too. Add the salt and half of the broken graham crackers and stir so the cracker pieces are incorporated into the chocolate marshmallow mixture but not broken up too much.
Tip the mixture into the prepared pan and press it into the pan with a wooden spoon. Sprinkle over the remaining graham crackers and marshmallows, pressing them down with your hands so they set into the base. Next, add the coated candies and sprinkles and press them down.
Allow to set for 1 hour before removing from the pan and cutting into bars. Or you can chill for 10 minutes and slice if you're in a hurry!