Heat the oven to 180C/fan 160C/gas 4. Mix the flour, bicarb, baking powder and salt in a bowl. Cream the butter, sugars, egg and vanilla with electric beaters. Stir in the flour mixture, then add the nuts, oats and chocolate.
Line 2 baking sheets with non-stick baking parchment and drop large tbsps of dough onto them. Press down gently. Bake for 8-10 minutes until light golden. Let cool for 5 minutes before transferring to a wire rack. underdone but will finish cooking on the hot tray. Wait until they are completely cool then pack into a tin lined with baking paper.