Start by preheating your oven to 350 degrees F and greasing a 9×13 pan (or lining it with parchment paper for easy removal).
In a large bowl, whisk together all of the wet ingredients: pumpkin puree, oil, maple syrup, applesauce, vanilla extract, and eggs until smooth.
Add the dry ingredients to the wet ingredients and stir just until combined. Fold in the chocolate chips, then pour the pumpkin bar batter into the prepared pan and spread it into an even layer.
Bake for 24-26 minutes, until the top of the bars is set, lightly golden, and a toothpick inserted in the center comes out clean. Let the bars cool completely before frosting – this gives you the best results and prevents melted frosting.
To make the frosting, beat the cream cheese, powdered sugar, and vanilla with an electric hand mixer or in the bowl of a stand mixer on low speed, then medium-high speed until fluffy. Add milk 1 tablespoon at a time until you reach a smooth, spreadable consistency. Use an offset spatula to spread the frosting evenly over the cooled bars, then slice and serve.