Heat oven to 325°F. Grease bottom and sides of 9x5" loaf pan with Magic Cake Release (see notes for link) or butter.
In a medium bowl, whisk flour, baking soda, baking powder and salt.
In a separate large bowl or bowl of electric mixer, mix mashed bananas, sugar, oil, eggs and vanilla.
Add flour mixture to banana mixture a bit at a time, stirring by hand or on low speed of a mixer until fully incorporated. Pour into prepared pan.
Bake 325°F for 60-70 minutes until wooden pick inserted in center comes out clean. Let cool 10 minutes in pan. Remove from pan and cool completely on wire rack. When cool, slice with a serrated knife.
Notes
Magic Cake Release: click for recipeTo easily mash bananas, use an electric mixer. Don't have a mixer? Use a fork or potato masher in a bowl, or mash them in a large baggie.