01 - Preheat oven to 350°F. Grease and flour a 9-inch round or square cake pan, then line the bottom with parchment paper for easy release.
02 - In a large mixing bowl, beat the mashed bananas, vegetable oil, sugar, eggs, and vanilla extract together until the mixture is smooth and well blended.
03 - In a separate bowl, whisk together the all-purpose flour, baking soda, baking powder, salt, and ground cinnamon until evenly distributed.
04 - Gradually fold the dry ingredient mixture into the wet ingredients using a spatula, mixing until just combined. Stop as soon as no dry streaks remain to keep the cake tender.
05 - Gently stir in chopped walnuts, pecans, or chocolate chips if desired, distributing them evenly throughout the batter.
06 - Pour the batter into the prepared cake pan and use a spatula to smooth the surface, ensuring an even layer.
07 - Bake on the center rack for 35 to 40 minutes, or until a toothpick inserted into the center of the cake comes out clean and the top springs back when lightly pressed.
08 - Allow the cake to cool in the pan for 10 minutes, then carefully invert onto a wire rack to cool completely before serving or frosting.