Step 1: Preheat your oven to 350°F (175°C) and line an 8×8 inch square baking pan with parchment paper, leaving a slight overhang on the sides for easy removal.
Step 2: In a large mixing bowl, whisk together the pumpkin puree, maple syrup, egg, and vanilla extract until the mixture is smooth and well combined.
Step 3: Add the rolled oats, pumpkin pie spice, cinnamon, baking powder, and salt to the wet ingredients. Use a spatula to fold everything together until all the oats are thoroughly coated.
Step 4: If using chocolate chips or nuts, gently fold them into the batter at this stage.
Step 5: Transfer the mixture into the prepared baking pan and spread it out evenly using the back of a spoon or a spatula, pressing down slightly to ensure it is compact.
Step 6: Bake in the preheated oven for 22-25 minutes, or until the edges are golden brown and a toothpick inserted into the center comes out clean.
Step 7: Remove from the oven and allow the pumpkin oatmeal bars to cool completely in the pan before lifting them out by the parchment paper and slicing into 12 even bars.