Spray a 9x13-inch baking dish with nonstick cooking spray; set aside.
In a saucepan over medium heat, melt butter and whisk in brown sugar, maple syrup and salt until smooth.
Remove from heat and fold in bananas; set aside.
Cut bread into 1-inch pieces and place half in the bottom of prepared dish.
Spread half the banana mixture on top. Repeat by topping with remaining bread and banana mixture.
In a large mixing bowl, whisk together egg whites, milk, maple syrup, protein powder, vanilla, cinnamon and salt.
Pour egg mixture evenly over bread, cover and place in fridge for at least two hours, but best overnight.
Preheat oven to 350 degrees F.
Uncover and bake for 55-60 minutes, or golden brown on top and set in the center.