Turn the oven on and set the heat to 350 degrees. Using your clean hand or a paper towel, lightly coat the loaf pan with the oil.
Put both flours, the baking soda, and salt in a large bowl and mix well. Set aside.
Put the bananas and sugar in the other bowl and mix until it’s as smooth as you can get it. There should be no big chunks of banana.
Add the butter, eggs, and vanilla to the banana mixture and mix well.
Add the flour mixture, a little at a time, and the nuts, if using, and mix well.
Once the oven temperature has reached 350 degrees, scrape the mixture into the prepared pan and carefully put it in the oven. Bake until firm in the center, about 1 hour.
Set aside to cool a bit, then remove from the pan. Once the bread has fully cooled, wrap in plastic wrap and then in wax paper, parchment paper, or wrapping paper. Tie with ribbon or twine.