Preheat oven to 325°F. Line two 9"x5" loaf pans with parchment paper in a sling fashion, then spray with cooking spray.
In a large mixing bowl, whisk together the all-purpose flour, white sugar, baking soda, baking powder, kosher salt, and cinnamon.
3 cups all purpose flour, 1 ½ cups granulated sugar, 1 teaspoon baking soda, 1 teaspoon baking powder, ½ teaspoon kosher salt, ½ teaspoon ground cinnamon
Stir in the mashed banana, vegetable oil, beaten eggs, and vanilla extract with a rubber spatula until combined.
2 cups mashed banana, 1 cup vegetable oil, 3 eggs, 2 teaspoons vanilla extract
Stir in half of the chopped walnuts.
1 cup walnuts
Pour batter into each prepared loaf pan, dividing it evenly. Sprinkle the remaining walnuts on top of the loaves, dividing equally. Bake 55–65 minutes, or until a knife inserted into the center comes out clean and the tops of the loaves are golden brown.
Let the loaves cool in the pans about 10 minutes before removing and transferring them to a wire rack to cool completely.