Preheat your oven to 350°F (175°C) and line a 12-cup muffin tin with paper liners or lightly grease with cooking spray.
Combine the wet ingredients in a large bowl – mashed bananas, pumpkin puree, eggs, maple syrup, milk, melted coconut oil, and vanilla extract. Whisk until smooth and well incorporated.
In a separate bowl, mix the dry ingredients – rolled oats, whole wheat flour, baking soda, pumpkin pie spice, and salt. Stir until evenly combined.
Gently fold the dry ingredients into the wet mixture using a spatula, being careful not to overmix. Stir just until no dry flour pockets remain – the batter should be thick but moist.
If using nuts or chocolate chips, fold them in now, reserving a small amount for topping if desired.
Divide the batter evenly among the prepared muffin cups, filling each about 3/4 full. Sprinkle any reserved toppings over the muffins.
Bake for 22-25 minutes or until a toothpick inserted into the center comes out clean with just a few moist crumbs.
Allow the muffins to cool in the pan for 5 minutes before transferring to a wire rack to cool completely.