Preheat your oven to 325°F (163°C). Prepare a 9×5-inch loaf pan with oil or parchment paper.
Mash the bananas in a large mixing bowl until smooth.
Add oil, eggs, and vanilla to the mashed bananas and whisk together.
Into the same bowl, add flour, baking soda, baking powder, salt, and cinnamon. Add any optional mix-ins if desired, and gently mix until just combined.
Pour the batter into the prepared loaf pan and smooth the top. Bake in the preheated oven for 60-75 minutes.
Check for doneness with a toothpick. Let the bread cool in the pan for about 10 minutes, then transfer to a cooling rack for another 15-20 minutes before slicing.
