Preheat oven to 350°F (175°C) and grease a 9x5 inch loaf pan with non-stick spray or parchment paper.

In a large mixing bowl, combine mashed bananas, peanut butter, honey, egg, and vanilla extract; whisk until the mixture is homogenous.

In a separate medium bowl, whisk together whole wheat flour, baking soda, salt, and ground cinnamon.

Gradually add the dry ingredients to the wet ingredients, folding gently with a spatula until just incorporated to avoid over-developing gluten.

Transfer the batter into the prepared loaf pan and level the surface with a spatula.

Bake for 50 to 60 minutes, or until a skewer inserted into the center of the loaf comes out clean.

Remove from the oven and allow to cool in the pan for 10 minutes before transferring to a wire rack to cool completely before slicing.