Preheat the oven to 350°F (175°C) and grease a 9x5-inch loaf pan.
In a large bowl, combine mashed bananas and vegetable oil.
Add sugar to the mixture, stirring until dissolved.
Mix in eggs one at a time, followed by vanilla extract.
In a separate bowl, sift flour, baking soda, baking powder, and salt.
Gradually add dry ingredients to the banana mixture, folding until combined.
Fold in chopped walnuts gently to avoid overmixing.
Pour batter into the prepared loaf pan, smoothing the top.
Bake for 60-70 minutes or until a toothpick comes out clean.
Allow the bread to cool in the pan for 10 minutes, then transfer to a wire rack.