Mix the Egg (1), Oil (1/4 cup), and Greek Yogurt (1/2 cup).
Peel and mash the Banana (5). You want 2 cups of mashed banana.
Mix the bananas with the yogurt mixture along with Milk (1/4 cup) and Vanilla Extract (1 teaspoon).
Add the Whole Wheat Flour (1 cup), All-Purpose Flour (1 cup), Baking Soda (1 teaspoon), Baking Powder (1/2 teaspoon), Granulated Sugar (1/2 cup), Salt (1/2 teaspoon) and chopped Walnut (1/2 cup).
Mix until combined.
Pour the batter into greased mini loaf pans or a 9 x 5 greased loaf pan. Sprinkle with a mixture of sugar and Ground Cinnamon (to taste) if needed.
Bake at 350 degrees F (180 degrees C) for about an hour until the bread is done. Use a tooth pick to check if the bread is done. If you use a mini loaf pan, bake for 20 to 25 minutes.
Let cool on a wire rack before serving. Enjoy!