Preheat oven to 350°. Spray two 8" round cake pans with cooking spray.
With electric mixer, beat cake mix, eggs, oil, water and sour cream on low till combined. Beat on high for 2 minutes.
Slice bananas. Place slices evenly on the bottom of each cake pan.
Melt butter in small pan. Add brown sugar and lemon juice, and heat till dissolved.
Pour half of brown sugar mixture into each of the cake pans, over the bananas.
Sprinkle coconut over brown sugar sauce.
Pour cake batter on top of the coconut into both pans, dividing equally.
Bake at 350° for 35-40 minutes.
Remove from oven and let sit five minutes.
Invert onto serving plates.
Slice and serve.
** SUGGESTION **
Instead of having two separate single-layer cakes, you might want to put one layer on top of the other (with the bananas in between the layers, just like frosting)! I think I'll try that next time. ☺