Preheat the oven to 350 degrees F. Line a 12-cup muffin pan with muffin liners and spray the inside of the liners with nonstick cooking spray to prevent sticking.
In a large bowl, whisk together the all purpose flour, white whole wheat flour, flaxseed meal, pumpkin pie spice, baking powder, baking soda, and salt until well combined.
In a separate large bowl, whisk together mashed banana, pumpkin, pure maple syrup, olive oil, milk, egg, and vanilla until well combined.
Add the dry ingredients to the wet ingredients and use a wooden spoon to mix together until the batter is just combined. DO NOT overmix. Fold in ½ cup chocolate chips and walnuts (or pecans), if using.
Divide batter evenly into muffin liners, then sprinkle each muffin with a few extra chocolate chips. Bake for 20-25 minutes or until the toothpick comes out with just a few crumbs attached.
Cool muffins for 5 minutes then remove from the pan and transfer to a wire rack to finish cooling. Muffins are best served warm and even better the next day.
