Preheat oven to 350 degrees F (175 degrees C). Grease and flour 2 (8 inch) pans.
Combine butter and brown sugar, divide and spread evenly between the 2 pans.
Sprinkle pecans evenly over both brown sugar mixtures, arrange banana slices evenly over each.
Prepare cake mix according to package instructions. Divide batter into the 2 pans.
Bake in the preheated oven for 40 to 45 minutes, or until a toothpick inserted into the center of the cake comes out clean. Turn cakes upside down on a platter or plate, gently tap bottom and carefully remove pans, replacing caramel mixture that sticks to pan.
