Preheat oven to 180°C. Coat two large baking trays with non-stick cooking spray.
Sift the plain and wholemeal flours, cinnamon, salt, bicarbonate of soda and allspice into a medium bowl.
Beat the brown sugar, honey, oil and egg white in a large bowl to combine. Stir in the puréed pumpkin. Stir in the flour mixture until evenly moistened. Fold in the dried cranberries and the walnuts, if using.
Drop heaped teaspoons of dough onto the baking tray, spacing them about 2.5 cm apart. Bake until a skewer or toothpick inserted in the centre of a biscuit comes out clean, about 15 minutes. Leave the biscuits on the tray for 1 minute. Use a metal spatula to transfer them to a wire rack to cool. Store in an airtight container for up to 1 week.