Preheat oven to 400F/ 200C. Line a regular-sized muffin tin with liners or spray with baking spray.
Sift the flours, baking powder and baking soda into a large bowl. Add the oats, ground flax seeds, cinnamon and salt and whisk everything to combine then make a well in the center and set aside.
In a separate medium bowl, mash the bananas. Squeeze a little of the moisture from the zucchini, then add to the bananas with the melted butter or oil and vanilla. Stir to combine then add to bowl of dry ingredients.
Fold everything together until almost all combined and toss in the chocolate chips and chopped walnuts. Fold a few more times until all the ingredients are combined. Divide batter evenly among prepared muffin cups.
Bake at 400F/200C for 10 minutes, then reduce the heat to 350F/177C and bake about 7-10 minutes more until the muffins spring back to the touch or a toothpick entered into the center comes out clean. Cool muffins in the pan 10 minutes. Enjoy.
*These muffins keep well in an airtight container at room temperature for a few days, refrigerated about a week or in the freezer for a couple months.