Preheat oven to 350 degrees. Grease & flour a 10" tube pan, making sure to get center post well covered.
In a medium bowl, mix pecan frosting and oats together. Set aside.
In a large mixing bowl, beat sour cream, eggs and mashed bananas together til smooth. Continue beating while adding in cake mix. Mic for 2 minutes at medium speed.
Pour 1/3 of cake batter (approximately 2 cups) into bottom of tube pan. It gets a little messy here but use your hands to crumble 1/3 of pecan-oat mixture on top. Repeat with two more layers ending with the pecan-oat mixture.
Bake 50-60 minutes or until pick in center comes out clean. Cool upright on wire rack.
When ready to remove, use a sharp knife and go around outside of cake then around center post so that when you invert it onto another wire rack it doesn't stick. Then invert back onto first rack so that pecan-oat mixture is on top.