In a high speed blender or food processor, add your frozen banana and blend until smooth. Add the cocoa powder and blend once more, until fully incorporated.
Transfer the low calorie ice cream mixture into a freezer friendly container and store in the freezer for at least two hours, to freeze. For the first hour, stir the mixture every 20 minutes, to ensure it doesn't become icy.
Remove the container from the freezer and let it sit at room temperature for 15 minutes, before scooping and serving.
Notes
Serving size: 1/4 of the recipe yields approximately 1/2 cup (60-65g).