Preheat your oven to 350°F. Line a loaf pan with parchment paper or spray it with nonstick baking spray.
Mash the bananas until they are mushy.
In a large bowl, combine the yellow cake mix, mashed bananas, melted butter, eggs, and vanilla extract. Stir until everything is combined and there are no lumps.
Pour the batter into a greased baking pan.
Bake for 50-60 minutes, or until a toothpick comes out clean when inserted into the center.
Allow the loaf to cool for 30 minutes or more before cutting into slices and serving!
Notes
Nutritional values may vary and are meant to be a guide.