In a medium size mixing bowl, mash the banana. Then stir in the egg, vanilla extract, and oil until combined. Then add all at once the flour, sugars, baking soda, and salt. Fold until combined. Then stir in the chopped walnuts.
If you use mini loaf pans (like I have in the photos), this will yield three and should be baked for 18-20 minutes.
I added a second banana to the top of these mini loafs just for the photos (just trying to give you something pretty to look at it). This is not necessary and in fact I found it caused the batter just under the banana to bake unevenly. So I really don't even recommend it, but if you want the look ... I get it. :)