Cut bananas into chunks and blend in a food processor until smooth. Put in a freezer-proof container and freeze until just frozen. Remove from the container and blend again to make a creamy frozen icecream-like consistency. Serve straight away, or freeze to serve later. Experiment with adding strawberries and other flavours. You could add 1tb honey and 1/4 tsp cinnamon to 4 bananas worth, or add a handful of berries.
Here is one I made by making the banana icecream, then splitting it into 2 batches, in one I added a handful of frozen blueberries, and the other I added a handful of frozen raspberries, then I poured them both into the one container and swirled them together.

YUM!
Banana On A Stick
Peel bananas and coat with a little orange juice. Stick a skewer into the banana as a stick and freeze for 20 mins. You can roll the bananas in crushed rice bubbles, nuts, sprinkles or coconut before freezing.