In a saucepan, combine mango, coconut (if using) and milk; bring to almost a boil over medium heat, stirring often. Stir in couscous; remove from heat, cover and let stand for 5 minutes.
Meanwhile, in a bowl, whisk together yogurt, brown sugar and vanilla.
Using a fork, gently stir bananas into couscous, fluffing couscous. Spoon into bowls and top with yogurt mixture.