Preheat oven to 350°F. Grease a loaf pan with non-stick cooking spray or grease with shortening and set aside.
Add the bananas to a bowl with the warm, melted butter and mash using a fork or potato masher.
Add the oil, buttermilk, beaten eggs, and vanilla. Mix well to combine.
In a second large bowl whisk together the flour, sugar, brown sugar, baking soda, and salt.
Add the nuts and pour the wet ingredients into the dry ingredients and mix together with a wooden spoon until combined (the mixture will be thick).
Spoon the mixture into prepared loaf pan and bake for 45-55 minutes until golden and a cake tester inserted in the center of the bread comes out clean.