Put the dates in a medium heatproof bowl with the bicarbonate of soda, then pour over 250ml boiling water and set aside to soak for 10 minutes. Drain well.
Preheat the oven to 180°C/fan160°C/gas 4 and line a 20x30cm brownie tin or baking tray with baking paper.
In a food processor, whizz the dates, peanut butter, egg whites and agave syrup until quite smooth. Transfer to a large bowl and stir through all the oats until they’re well coated.
Press the mixture evenly into the prepared tin, then bake in the middle of the oven for 20 minutes until golden and crisp on top. Leave to cool completely in the tin, then transfer to a chopping board and cut into 16 squares.