I found it on the Girl Who Ate Everything Blog! You can click the blog title to view her recipe. I've also copied it below with a few minor changes I made. Give it a try :)
It was so easy to make and looks pretty fancy. Full disclosure though, when I turned it out of the pans only about 5 bananas stayed on the cake. The rest were easy enough to pull out of the pan though and place back on the cake. The caramel like topping is still creamy enough that the bananas sink back into place and look fab. So give it a try!
Banana Coconut Upside Down Cake
1 yellow cake mix (I used Duncan Hines)
1/3 cup oil
1/2 cup sour cream
small box of instant vanilla pudding mix
6-7 bananas (sliced 1/4 in. thick)
2 cups shredded coconut
1/2 cup butter
1 cup packed brown sugar
2 T. lemon juice
Preheat oven to 350 degrees. In a large stand mixer, combine cake mix, eggs, oil, sour cream, water and instant pudding mix.
Grease two 8 or 9 inch round cake pans. (She suggests 8 in. but I used 9 and it turned out fine. If you have 8 in. pans it would probably make the topping thicker) Layer bottom of both pans with sliced bananas.
In a small saucepan, melt butter and add brown sugar and lemon juice. Stir until completely melted and combined. Pour sauce over bananas. Top each pan with 1 cup of the shredded coconut.
Divide cake batter in half and pour into each pan. Spread evenly. Bake at 350 degrees for 35-40 minutes. Let rest 5-10 minutes and invert on serving plate. As I said above, many of the bananas might stay in the pan simply pull them out and arrange on cake. Enjoy!