Preheat your oven to 350°F (175°C) and grease a 9x5-inch loaf pan.
In a large bowl, mash the ripe bananas until smooth. You should have about 1 1/2 cups of mashed bananas.
Add the olive oil, brown sugar, vanilla extract, and egg (or flax egg) to the bowl with the bananas. Mix well until combined.
In a separate bowl, whisk together the flour, baking soda, salt, and cinnamon.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Be careful not to overmix, as this can lead to a dense bread.
If using, fold in the nuts and seeds at this point.
Pour the batter into the prepared loaf pan and smooth the top with a spatula.
Bake for 50-60 minutes or until a toothpick inserted into the center comes out clean. The top should be golden brown.
Once baked, remove the banana bread from the oven and let it cool in the pan for about 10 minutes before transferring it to a wire rack to cool completely.