Pre-heat the oven at 360° F (180° C).Mash the 3 ripe bananas with a fork in a bowl and then add the oil, eggs, syrup, vanilla extract, yogurt and sugar until combined. Once ready, add all the dry ingredients: flour, oats, baking powder, baking soda, salt and cinnamon. Lastly, add the walnuts and mix it with a spatula.
Prepare a non-stick loaf pan (9" x 5" (23.5cm x 13.2cm)) with parchment paper and pour the batter. Cut the banana lengthwise and add each half to the top of the batter. Bake for 50 mins o 1 hour at 360°F (180°C), or until golden. To see if is cooked, insert a toothpick into the center and it should come out clean.