Preheat oven to 180 deg Celsius or 350 deg Fahrenheit.
Prepare a 9x5 loaf pan with parchment paper.
In a wide mixing bowl , combine whole wheat flour , all purpose flour , Oats , sugar , cinnamon powder , salt , baking powder and cooking soda.
Mix well everything and set aside.
Take another bowl , add banana and mash well with a fork.
Add milk , yogurt , oil , vanilla essence and whisk well together.
Now slowly add dry ingredients into wet ingredients mixing gently with a spatula. Just combine everything , don't over mix .
Pour batter into prepared bread tin , tap gently .
Place in oven and bake for about 48 -50 minutes or until a toothpick inserted comes out clean.
Cover the pan with aluminium foil and set aside to cool. This is a optional step but steam from cake helps to soften the top crust giving a nice texture on top.
When still warm, remove from tin , cut into a thick slice and serve with plain butter.
Store at room temperature / refrigerate wrapped in cling wrap for up to 3 days.