Preheat oven to 350*. Grease and flour 2 (8") round cake pans or a 9x13" casserole. Combine butter and brown sugar, divide and spread evenly between the 2 pans or spread it all in 9x13 pan. Sprinkle pecans evenly over brown sugar mixture. Arrange banana slices evenly over pecans. Prepare cake mix according to package instructions. Divide batter into the 2 pans (or pour evenly over pecans in 9x13). Bake 40-45 minutes, or until a toothpick inserted into the center of the cake comes out clean. Turn cake(s) upside down on a platter or plate, gently tap bottom and carefully remove pans, replacing caramel mixture that sticks to pan. A few pear slices can be added to bananas for extra flavor.