Preheat oven to 180 degree C. Grease a 9X5 inch nonstick loaf pan with oil or nonstick cooking spray and set aside. If you have normal pan, oil it well and dust with flour and set aside.
Now in a bowl, take flour, baking soda, baking powder, cinnamon and salt and mix well.
Now in a bowl, take butter, oil, sugar, and mix well. Add in eggs and beat well.
Now add in bananas and mix well.
Now add in the flour mix and fold gently, add in flax seeds and walnuts and fold gently,
Spoon this into the baking pan and bake for 55 mins to 60 mins.
Remove it and cool it down completely. Now unmould it and cool down completely.