Preheat your oven to 350°F (175°C). Grease a 9x5x2.5-inch loaf pan and line it with parchment paper, leaving a little overhang on the sides for easy removal.
In the bowl of a stand mixer fitted with the paddle attachment, or in a large mixing bowl using an electric hand mixer, combine the mashed bananas, yogurt or sour cream, sugar, oil, eggs, and vanilla. Mix on medium speed until everything is well blended and smooth.
In a large bowl, whisk together the flour, oats, baking powder, baking soda, salt, and cinnamon until everything is evenly mixed.
Stir the dry ingredients into the banana mixture just until combined—don’t overmix. Pour the batter into the prepared loaf pan and smooth the top. If you like, sprinkle a few extra rolled oats over the top for texture and a rustic look.
Bake in the preheated oven for 70–75 minutes, or until a toothpick inserted into the center of the loaf comes out clean.
Let the bread cool in the pan for about 10 minutes, then use the parchment paper to lift it out onto a wire cooling rack. Allow it to cool completely before slicing for the best texture and clean cuts.
