Preheat oven to 350 degrees F. and line 9x13 inch baking dish with parchment paper lightly sprayed with cooking spray.
Place pumpkin and cake mix into a large mixing bowl, stir until well combined. Transfer half of the mixture into prepared baking dish spreading evenly. Top evenly with 4 graham crackers, then chocolate bars on top of graham crackers. Top evenly with marshmallows then scoop remaining dough over marshmallows with a medium cookie scoop. Bake for 25-30 minutes, until baked through. Remove and let cool completely. Cut into square and serve room temperature.