Prepare the banana filling by heating butter in a nonstick saucepan over medium heat.
Add brown sugar, cinnamon powder and mix until sugar dissolves completely.
Add apple juice, vanilla extract and cook for 1-2 minutes or until mixture thickens a bit.
Remove from heat and pour this sugar mixture in an oven-safe rectangle baking dish (Dimensions: 7x11 or 8x12).
Add banana chunks and mix them gently so they are coated in the sugar mixture.
Spread them out evenly in the dish. Keep aside.
Prepare the topping by mixing together oats, flour, brown sugar, butter, cinnamon powder, vanilla extract in a large bowl. Use a pastry cutter or a large fork to cut the butter into the flour/oat mixture until you have a crumbly mixture. Do not add milk or water to thin it out.
Stir in chopped pecans.
Spread this mixture on top of the banana filling evenly.
Bake at 350 degrees F for 20-25 minutes or until topping is golden brown.
Remove from oven and let it cool for about 15 minutes.
Then, serve with whipped cream.