Turn on the oven and set the heat to 350 degrees.
Put the flour, cocoa powder, baking soda, and salt in a bowl and mix well. Set aside.
Put the bananas and sugar in a bowl and mash mash mash until the mixture is completely combined and there are no big chunks of banana. If you have a mixer, add them to the mixer and turn it on and whip for 2-3 minutes.
Add the butter, eggs, and vanilla extract and mix well.
Add the flour mixture, a little at a time and mix by hand, with a spatula or large spoon until well combined. If you dump the flour in too quickly, it will poof up out of the mixer!
Add the nuts, if no one is allergic to them.
Pour the mixture into the prepared pans and, once the oven temperature has reached 350 degrees, put them in the oven.
Bake until firm in the center and a toothpick inserted comes out with a bit of crumb on it, 35-40 minutes. (Time is one hour if you use a standard loaf pan).