01 - Preheat oven to 350°F. Grease and flour a 9-inch round or square cake pan.
02 - In a large mixing bowl, beat the mashed bananas, oil, sugar, eggs, and vanilla extract until smooth and well blended.
03 - In a separate bowl, whisk together the flour, baking soda, baking powder, salt, and cinnamon if using.
04 - Gradually fold the dry ingredient mixture into the wet ingredients until just combined. Be careful not to overmix.
05 - Gently stir in the chopped nuts or chocolate chips if desired.
06 - Pour the batter into the prepared cake pan and smooth the surface evenly with a spatula.
07 - Bake for 35 to 40 minutes, or until a toothpick inserted in the center comes out clean.
08 - Allow the cake to cool in the pan for 10 minutes, then transfer to a wire rack to cool completely before serving.