Preheat oven to 350 degrees F.

To a small skillet over medium heat, add walnuts. Cook until lightly toasted.

Into a food processor, add bananas. Pulse 10 times, until mostly smooth but some chunkiness still remains.

Add vegetable oil, sour cream, lemon juice, and vanilla bean paste. Pulse 4 more times to combine.

Into the flour mixture, gently fold in the banana mixture, just until blended.

Into a prepared 9"x5" loaf pan, pour all the batter and smooth the top.

Bake 1 hour. After removing from oven, allow bread to stand in pan 10 minutes then remove from pan and transfer to a wire rack. Cool completely before slicing and serving.