Preheat the oven to 350℉/177℃. Place liners in a muffin pan. If you don't have liners, grease the pan liberally. Alternatively, you can use a silicone pan without liners.
In a large bowl, whisk together the mashed bananas, pumpkin, eggs, maple syrup, avocado oil, and vanilla extract.
In a measuring cup or separate bowl, stir together the whole wheat flour, pumpkin pie spice, baking powder and soda, and salt.
Add the dry ingredients to the bowl with the wet ones. Gently stir with a rubber spatula until just combined. Fold in the chopped walnuts.
Use a ¼-cup measuring cup to scoop the batter evenly into the liners.
Bake for 20 to 24 minutes until a toothpick inserted in the center of one of the muffins comes out clean.
Let the muffins cool in the pan for a few minutes before transferring to racks to cool completely. Enjoy warm or fully cooled!
Leave a rating or review by tapping the stars on this recipe card (above) or in the comments section (at the end of the post)!