Step 1: Preheat your oven to 350°F (175°C). Lightly grease a 9x13 inch baking dish.
Step 2: In a large bowl, combine the pumpkin puree, yellow cake mix, and melted butter. Mix with a spoon or spatula until well combined and no dry streaks of cake mix remain.
Step 3: Gently fold in the chocolate chips until evenly distributed throughout the batter.
Step 4: Press the mixture evenly into the prepared baking dish. The batter will be thick.
Step 5: Bake for 20-25 minutes, or until the edges are golden brown and a toothpick inserted into the center comes out clean or with moist crumbs.
Step 6: While the bars are cooling, prepare the glaze. In a small bowl, whisk together the powdered sugar and milk until smooth and creamy. If too thick, add a tiny bit more milk; if too thin, add a bit more powdered sugar.
Step 7: Once the bars have cooled completely, drizzle the glaze evenly over the top.
Step 8: If desired, sprinkle with chopped nuts and granola. You can also add fresh whipped cream and a chocolate drizzle for extra garnish before serving. Slice into bars and enjoy!