Preheat oven to 350 degrees F. Grease 9 x 5″ loaf pan and set aside.
Cream butter and sugars together with an electric mixer on medium-low speed until fluffy.
Turn speed to low, and mix in eggs one at a time until combined. Stir in vanilla, mashed bananas, and sour cream on lowest speed.
In a small bowl, mix together flour, oats, baking soda, and cocoa powder. Add dry mixture to wet ingredients and stir on lowest speed just until combined. Gently fold in chocolate chips.
Pour batter into prepared pan and bake in preheated oven for 75 minutes, or until toothpick inserted into center comes out clean. Cool in pan for 15 minutes, then transfer to wire rack to cool completely before cutting.