Preheat the oven to 375°F. Place an oven rack in the centre position.
Slice the bread into 1-inch slices and then cut then slices into 1-inch cubes. You can also tear the bread apart with your hands. Leave the crusts on.
Lightly grease a 7x11 inch (if you want thicker slices) or 9x13 inch baking dish (if you want thinner slices) with cooking spray. Add enough bread cubes to cover the bottom of the dish. Sprinkle half the blueberries on top. Repeat again, layering the bread chunks and blueberries. In a medium bowl or measuring cup, mash the bananas. Whisk in the eggs, milk, vanilla, 1/2 teaspoon of cinnamon, and salt; mix well. Pour the egg and milk mixture evenly over all the bread chunks.
At this point, the casserole can be baked right away, or covered and refrigerated overnight.
In another small bowl, mix together the melted coconut oil or butter with the coconut sugar, 1 teaspoon cinnamon, and pinch of salt. Using a spoon, drizzle the mixture evenly over all the bread chunks and blueberries.
Bake the casserole, uncovered, for 35 to 45 minutes. I baked mine for about 40 minutes. Leave the casserole in the oven longer if you want the chunks of bread on the top to be more brown and crispy.
Let the casserole cool for about 10 minutes before serving. Serve with maple syrup, if desired.