Place the chopped dates into a heatproof bowl and cover with 110ml (4fl oz) boiling water. Set aside and leave to soak for half an hour.
Meanwhile, place the walnuts, sunflower seeds and dark chocolate into a food processor and pulse to roughly chop into small chunks. Transfer to a large mixing bowl.
After the dates have been soaking for 30 minutes, transfer to the food processor and blend to a purée. Add the date purée to the walnut mixture along with the rest of the ingredients. Mix and combine. Preheat the oven to 130oC/Gas Mark 1.
Transfer to a brownie tin lined with greaseproof paper and bake in the oven for 35-40 minutes until golden brown.
Leave in the tin to rest for a few minutes, before using the edges of the greaseproof paper to lift the flapjacks out. Transfer to a wire rack to cool completely.