Preheat your oven to 350°F (175°C).
Grease a 9x5-inch loaf pan lightly with butter or cooking spray.
In a large mixing bowl, combine the mashed bananas, Greek yogurt, granulated sugar, brown sugar, eggs, and vanilla extract. Mix until smooth.
In another bowl, whisk together the baking soda, baking powder, salt, flour, and cinnamon (if using).
Fold the dry ingredients into the wet mixture until just combined.
If desired, fold in chopped walnuts or chocolate chips.
Pour the batter into the prepared loaf pan and smooth the top. Bake for 50-60 minutes.
Let the bread cool in the pan for about 10 minutes before transferring it to a wire rack.