Preheat oven to 350 degrees F. Prepare baking sheets by lining them with parchment or greasing well.
Place Steel Cut Porridge Oats in a bowl and pour boiling water over. Stir, then cover bowl with a large dinner plate; let stand 10 minutes. Spread Porridge Oats out over dinner plate. Cool 2 minutes, then transfer plate to freezer to cool completely to room temperature (about 10 minutes total).
Meanwhile, combine butter and sugars in a standing mixer; beat until light and fluffy. Beat in egg and vanilla.
In a separate bowl, whisk together flour, baking powder, baking soda, salt and cinnamon. With mixer speed on low, gradually add flour mixture to butter mixture, beating until combined. Incorporate cooled Steel Cut Porridge Oats, carrots, raisins and walnuts.
Drop by tablespoonfuls onto prepared cookie sheets, leaving about 2 inches between them. Bake 8-10 minutes, until centres of cookies are set.