Preheat the over to 350° Fahrenheit (180° Celsius).
Prepare a loaf pan by greasing it with sunflower seed oil or coconut oil.
In a medium mixing bowl, using a metal spoon, mix sunflower seed oil and coconut oil with brown sugar.
Add sour cream and continue mixing.
Add eggs, one by one, and continue mixing.
Then add salt, vanilla extract, and cinnamon if you like.
Mush the bananas using a fork and add them to the mixed ingredients. Mix them all together.
Chop the walnuts and add them to the mixture and mix them with the banana batter.
In a separate mixing bowl, mix together flour with baking soda.
Slowly combine the mixed flour with the wet banana and walnut mixture and gently stir until the batter is uniform.
Pour the mixture into the loaf pan.
Bake for about 45 minutes. Check with a toothpick if the bread is fully baked in the middle. If the toothpick comes out wet, add another 5 - 10 minutes.
Let it cool for 10 - 15 minutes. Enjoy with a cup of tea or coffee, or serve it toasted for breakfast with some butter. Yum!