Start by preheating your oven to 350°F (175°C). Grease a 9x5-inch loaf pan or line it with parchment paper.
In a medium bowl, whisk together the whole wheat flour, baking soda, baking powder, salt, and cinnamon.
In a large bowl, mash the ripe bananas. Add the Greek yogurt, vegetable oil, honey or maple syrup, eggs, and vanilla extract. Mix until well combined
Gradually add the dry ingredients to the wet mixture, stirring until just combined. Be careful not to overmix.
Pour the batter into the prepared loaf pan and smooth the top with a spatula.
Fold in the chopped walnuts, or decorate them on top.
Bake for 50-60 minutes, or until a toothpick inserted into the center comes out clean.
Allow the bread to cool in the pan for about 10 minutes, then transfer it to a wire rack to cool completely.