Preheat the oven to 350 degrees.
Put the banana in the oven and roast for about 15 minutes, until it turns black and soft.
Remove the banana and lower the oven temperature to 325 degrees.
Let the banana sit until cool enough to handle.
Peel, transfer the flesh to a small bowl, and mash it with a fork.
Set aside.
Put the egg substitute into a mixing bowl and whisk until frothy.
Whisk in the buttermilk.
Add the cocoa powder, brown sugar, vanilla extract, mashed banana, and cooked rice, whisking after each addition.
Spray a 1 quart glass casserole once lightly with vegetable oil spray, and distribute the oil evenly over the surface.
Transfer the pudding mixture to the casserole and bake for 45 minutes.
Remove the pudding from the oven and let it sit for about 10 minutes before serving.
The pudding can be served warm or at room temperature.