Place an oven rack in the center position. Heat the oven to 350° F. Lightly grease an 8x4 loaf pan. Set aside.
To toast the walnuts, spread them onto a rimmed baking tray and place in the preheating oven. Take them out when fragrant and golden, about 5-8 minutes. Remove from the oven and transfer the walnuts to a bowl to cool.
In a medium bowl, whisk together the flour, baking soda, salt, and cinnamon.
2 cups (252 g) whole wheat flour, 1 tsp baking soda, ½ tsp table salt, ½ tsp cinnamon
In a large bowl, mix together the mashed banana, sugar, oil, Greek yogurt, eggs, and vanilla.
1 ½ cups (370 g) mashed banana, 6 TBS (144 g) brown sugar, 6 TBS (84 g) neutral oil, ¼ cup (62 g) Greek yogurt, 2 eggs, 1 tsp vanilla
Add the dry ingredients to the wet ingredients and mix gently until just combined.
Fold in the toasted chopped walnuts.
½ cup chopped walnuts, toasted
Pour the batter into the prepared loaf pan. Evenly sprinkle a layer of coarse demerara sugar over the top if you want.
Bake for 50-55 minutes. Let bread cool in the pan for 10 minutes, then transfer to a wire rack and let cool completely.