Preheat oven to 350 degrees and lightly grease one 9x5" loaf pan or three 3x5.75" mini loaf pans.
In a large mixing bowl, cream together butter and sugars until smooth and fluffy. Add egg, mayo, and vanilla, and mix again until smooth.
Add your bananas and mix until well incorporated. The mixture will look a little watery and separated at this point, but don't worry: that's normal.
Add flour, salt, baking powder, and baking soda to the bowl and mix just until evenly incorporated. Fold in chocolate chips and walnuts.
Pour batter into large loaf pan or divide evenly between mini-loaf pans.
Bake for 50-60 minutes for large loaf pan or 40-50 minutes for mini loaf pans, or until toothpick inserted into the center of the loaf comes out clean.
Notes
If using frozen bananas, let thaw completely before adding.Adapted from TI2GR on Allrecipes.com