Preheat the oven to 350°F and line an 8×8-inch square baking pan with parchment paper. In a large mixing bowl, combine the rolled oats, oat flour, baking powder, pumpkin pie spice, cinnamon, and salt. Give it a good stir to mix everything together.
In a separate medium bowl, whisk the egg, then add the pumpkin purée, mashed banana, maple syrup, and vanilla extract. Stir until smooth and well combined.
Pour the wet ingredients into the bowl with the dry ingredients and mix until everything is evenly incorporated. Gently fold in the chocolate chips, if using.
Spread the mixture evenly into the prepared baking pan, smoothing out the top. For a little extra chocolate in every bite, sprinkle a few more chocolate chips over the surface.
Bake for 20–25 minutes, or until a toothpick inserted in the center comes out clean. Let the bars cool in the pan for at least 15 minutes.
Once cooled, lift the baked oatmeal out of the pan using the parchment paper and slice into 12–16 bars. Store in an airtight container in the fridge for up to 4 days, or freeze for up to 3 months.