Line a 9x5-inch loaf pan with parchment paper or use a non-stick cooking spray.

In a small skillet over medium heat, toast the walnuts until lightly browned. Set them aside.

In a medium bowl, whisk together the flour, sugar, baking soda, and salt. Stir in the toasted walnuts.

In a large bowl, mash the bananas, leaving some chunks for texture. Using a wooden spoon, stir in the oil, sour cream, lemon juice, and vanilla bean paste with the mashed bananas.

Gradually fold the dry ingredients into the banana mixture until just combined.

Pour the thick batter into the prepared loaf pan and smooth the top with a spoon.

Bake for 1 hour. Let the bread cool in the pan for 10 minutes before transferring it to a wire rack to cool completely.

Use a bread knife to cut the loaf into individual slices and serve.