Preheat the oven to 350 F. Peel off the bananas and mash them with a fork.
Add mayo, egg, and vanilla extract. Stir until combined. Set aside.
In another bowl, mix together all-purpose flour, sugar, baking powder, and salt.
Pour the wet ingredients into the dry. Add chopped walnuts. Stir together just until combined.
Line a 9x5-inches loaf pan with parchment paper. Leave some paper hanging over on both sides for easy removal. Spray with non-stick cooking spray. Transfer the batter to the prepared loaf pan and spread evenly. Bake in the preheated oven for 60 minutes or until ready.
Check the readiness of the banana bread using a toothpick inserted in the center, if it comes out clean, the banana bread is ready. Remove from the oven. Let it cool, then slice and serve!