Preheat oven at 350°F. Grease a 9x5 or an 8 ½ by 4 ½ inch loaf pan and line bottom of pan with a strip of parchment paper.
Thoroughly whisk together flour, flax, sugar, baking powder, baking soda and salt. Set aside.
In a separate bowl, whisk together the eggs, oil and vanilla.
Add the bananas and flour mixture alternately to the egg mixture, stirring until blended. It will be very thick. Stir in the nuts.
The bake time might vary a bit between ovens and loaf pans. Check your bread as early as 35 minutes. The bread may take up to 60 depending on your loaf pan size, oven and the temperature of the batter. My original bake time was 55 to 60 minutes.
Let cool for about 20 minutes before loosening from pan. Remove from pan and let cool completely before slicing.