Preheat oven to 350°F (175°C). Grease or line a 9x5-inch loaf pan with parchment paper.
Mash bananas in a large mixing bowl until mostly smooth.
Add oil, sugar, milk, and vanilla to the mashed bananas. Mix until well combined.
Sift in flour, baking soda, salt, and cinnamon. Gently mix until no dry flour remains.
Fold in any optional add-ins, like walnuts or chocolate chips.
Pour batter into loaf pan and smooth the top.
Bake for 50–60 minutes, or until a toothpick inserted in the center comes out clean.
Cool for 10 minutes in the pan, then transfer to a wire rack to cool completely before slicing.