Peel the bananas, cut them in half, put them in a zip-lock bag and stick them in the freezer until completely frozen.
Wash beet well, peel it, and chop it in half.
Bring a small pot of water to a boil.
Add the beet to the boiling water and cook until soft when poked with a fork, about 20 - 25 minutes.
When cooked through, drain the water and allow the beet to cool.
Chop the beet up when it's cool enough to handle, place it in a tupperware container and freeze it for at least 2 hours.
Place all ingredients in a blender and blend until completely smooth. Add extra liquid as necessary – I like my smoothies thick but add almond or coconut milk if necessary.