Mix dry ingredients in one bowl. Mash bananas in another and then add mayo., egg, vanilla and sugar. Mix those well in another bowl. Then combine the two.
It will be a bit lumpy and that is okay, I don't like mashing my bananas until they are completely smooth, I'd rather have some chunks.
Preheat oven to 350 degrees F.
Use a 9x5 loaf pan, lay a piece of parchment paper down so it drapes over the sides. Pour in batter and bake for 40 minutes. Then place a piece of parchment or foil on the top so it doesn't get too browned and bake for another 10 minutes.
Put long toothpick in center and it should come out without wet batter, but with wet crumbs attached possibly. That is perfect.
You don't want to overbake it so once it is at this point, remove pan, lift loaf out by lifting sides of parchment paper and put that on a cooling rack and wait until cooled to slice.
Video
Notes
If making muffins, fill muffin liners 3/4 of the way full and bake for 18-20 minutes until center springs back when gently touched. Remove muffins from hot pan and cool on a cooling rack for moistest outcome.