Preheat oven to 350* Fahrenheit. Spray or grease and flour two deep 8-inch round cake pans. (I think my cake pans are 8 inches round by 2 inches deep, and I had just barely enough space for the risen cake.)
In a large bowl, using an electric mixer, beat the cake mix, eggs, oil, water and sour cream on low until combined. Increase speed to high and beat for 2 minutes.
Slice bananas evenly over the bottom of the two cake pans.
In a small saucepan, melt the butter. Add the brown sugar and lemon juice and heat until dissolved. Pour half of the brown sugar mixture into each of the two cake pans, over the bananas. Sprinkle coconut over the brown sugar sauce.
Pour the cake batter on top of the coconut, dividing equally between the two pans.
Bake 35-40 minutes or until cake tests done with a toothpick. Remove from oven and let cool for 5 minutes. Invert onto serving platter. Slice to serve.
Cake is probably best the day it is served, but leftovers can be stored overnight in the refrigerator. Much beyond that and the bananas might not be as appealing as you would wish.