Before freezing, peel the bananas and cut them into slices about 2 cm thick. Freeze for at least 5 hours.
Remove frozen banana pieces from the freezer and let them thaw a little. Place the bananas in a tall mixing bowl and puree with a hand blender (or in a blender jug). Add the remaining ingredients and mix in. Immediately fill into glasses or bowls and serve. Decorate with grated coconut if desired.