First make the sauce by bringing cocoa, sweetener, and milk to a boil in a small saucepan. Reduce heat and cook until slightly thickened while stirring constantly. Remove from heat and set aside.
In a food processor, blend bananas, milk, and vanilla until smooth.
Portion banana mixture into four serving bowls. Drizzle sauce on top of banana cream and serve immediately.
Notes
Fresh fruit can be used in place of chocolate topping.