Preheat the oven to 350 degrees F. Line an 8x8-inch baking dish with parchment paper so that you have some overhanging the sides like "handles," then lightly coat with cooking spray. Set aside.
With an electric mixer in a large mixing bowl or in the bowl of a stand mixer fitted with a paddle attachment, beat together the peanut butter, honey, applesauce, and vanilla extract until smooth and evenly combined, about 3 minutes. Beat in the salt.
Sprinkle the cinnamon, baking powder, and baking soda over the top. Then, sprinkle on the flour and oats. Beat until combined and the batter comes together With the mixer running on low speed, drizzle in the milk and continue beating until incorporated. The batter will be very thick. With a wooden spoon or spatula, fold in the chocolate chips.
Once dough is well combined, scrape it into the prepared baking dish, then press the top to make it even. Bake for 16-19 minutes, until the bars are lightly golden and just set. Do not over bake! Allow to cool completely, remove from the pan using the parchment paper overhang, then slice.
Store leftover bars in the refrigerator for up to 2 weeks or wrap tightly and freeze for up to 2 months.