Preheat oven to 190 degrees Celsius (375°F). Ideally, use square baking pan (about 22cm or 9-inches). I used too big baking dish and therefore the cake came up too low. So try to use a smaller dish. Spray the dish with the cooking oil.
In a bowl, mix the flour, baking powder, baking soda, and cinnamon.
In a separate bowl, whisk the eggs, sugar, yogurt, banana, oil, and vanilla.
Add this mixture to the flour mixture and mix well. Stir in walnuts. And pour the batter into the pan.
Bake in the oven for about 20 minutes or until a wooden pick inserted in the cake comes out clean.