Lightly grease 4 mini loaf pans or 1 standard loaf pan. Turn on the oven and set it 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 until the mixture is completely combined and there are no big chunks of banana. If you have a mixer, add them to the mixer, 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. Pour the mixture into the prepared pans and 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).