Preheat the oven to 200 C / Gas 6. Grease a medium baking tin and line with baking parchment.
Blitz the dates in a food processor for 30 seconds, then add the walnuts, bananas and seeds and blitz for a further 2 minutes.
Transfer the mixture to a mixing bowl and add the oats and mix well. Spoon into the prepared baking tin and gently press down with the back of a spoon to compact.
Bake in the preheated oven for 30 minutes until firm and golden brown. Remove from the oven and mark into squares. Allow to cool completely in the tin before removing and slicing into squares and serving.