Preheat oven to 325°F and line a loaf pan with parchment paper.
In a medium stock pot, heat walnuts over medium heat until lightly toasted (3-5 minutes).
Add sugar and turn up the heat to medium-high.
Cook, constantly stirring until sugar beings to clump and caramelize. When you have an amber liquid coating the nuts, pour onto a silicon mat to cool and sprinkle with salt.
In a stand mixer, whip eggs with sugar on high speed for 5 minutes until light and fluffy.
Turn mixer down to low-medium and slowly drizzle in olive oil until emulsified.
Add sour cream, vanilla, and ripe bananas and mix until combined.
In a large bowl, sift together flour, baking soda, salt, and cinnamon. Break apart the cooled walnuts and add to the flour mixture.
With a spatula, fold the flour mixture into the wet ingredients, 1/3 at a time, until incorporated.
Bake for 55-65 minutes until cake is golden and springs back when touched.