Peel the bananas and break them into your blender. Halve the avocado and scoop out the stone. Use a spoon to scoop the flesh out and into the blender. Add 1 tbsp tahini.
Pour in 330ml oat drink. Add a handful of ice cubes and blitz till smooth. Trickle in a little cold water if needed for a slightly thinner texture. Pour the smoothie into a couple of glasses and serve.