Preheat the oven to 375 degrees F.
Grease a metal loaf pan or line it with parchment paper.
In a large mixing bowl, mash your overripe bananas with a fork until they are an applesauce texture. Add the grated carrots, milk, butter, both sugars, maple syrup, vanilla, baking powder, baking soda, salt, and pumpkin pie spice to the bowl and mix well. Then, add the flour and mix until a thick batter forms.
Pour the batter into the prepared metal loaf pan and bake in the oven for 45-50 minutes or until the top of the loaf is golden and it is completely baked through the center.
Remove from the oven and allow it to cool. While the carrot cake banana bread is cooling, use an electric hand mixer or whisk to prepare the cream cheese frosting. Mix the softened butter, cream cheese, and powdered sugar together in a bowl and then spread it over the carrot cake banana bread.
Serve warm or cooled.