Preheat the oven to 350F. Line a loaf pan with parchment paper.
Whisk together the dry ingredients for the banana bread in a medium bowl (flours, baking powder and soda, salt, cinnamon) and set aside.
Mash the bananas in a large bowl. Add the eggs, oil, maple syrup, applesauce, and vanilla and beat on medium speed until combined.
Add the dry ingredients to the wet and mix on low speed (with a paddle attachment if available) until just combined.
Pour the batter into the lined loaf pan and set aside while you make the topping.
Combine all walnut topping ingredients together in a small bowl, starting with 1 tablespoon of oil. If the crumble is too dry, add the second tablespoon.
Crumble the topping evenly over the banana bread and bake for 50-55 minutes or until a toothpick comes out clean.
Let the loaf cool in the pan for 10-20 minutes before using the edges of the parchment paper to remove it to a wire rack to finish cooling.
I find that the longer you can wait to slice into it (even overnight), the better it tastes. This seems to let the flavors really develop.