Spray a 9x13 inch baking dish with cooking spray. Dice the bread slices in to 1 inch cubes. Evenly distribute the bread cubes into the baking dish.
Next, in a large bowl mash the bananas until mostly smooth with a few lumps remaining. Whisk in the eggs, almond milk, cinnamon, and vanilla extract.
Pour the mixture evenly over the cubed bread until all of the bread pieces have been coated in the egg mixture.
Place in the fridge for at least 30 minutes to allow the bread to absorb the liquid.
Evenly distribute the blueberries throughout the mixture, pressing into the top and down to the bottom so blueberries are incorporated throughout the casserole. Either place back in the fridge overnight, or bake immediately.
When ready to bake, preheat the oven to 350 degrees F. Bake for 40-45 minutes or until cooked through and bread is lightly browned.
Serve warm with maple syrup or additional blueberries and banana slices, if desired.