Preheat oven to 350 degrees.
Combine cake mix, pineapple w/ juices, milk, eggs, and oil. Beat with mixer until combined. Add bananas & mix 2-3 minutes.
Pour into a lightly greased 9x13 cake pan. Bake for 35 min, or until a toothpick comes out clean.
For the last 5 minutes, prep the topping: add brown sugar, butter, and 2 TBSP milk into a sauce pan. Stir over medium heat until bubbly. Turn off the heat & add the coconut mixture. Stir until mixed thru.
Pour hot mixture onto cake, spreading it all over in an even layer. Adjust the oven rack to broil position and carefully broil the topping until it has browned all over. ***be careful!! This stage can burn very easily!!!