Place the oats into a food processor or blender and grind into a fine powder. Stir the oats together with the plain flour, wholemeal flour, salt, baking powder and bicarb soda; set aside.
Beat the butter, apple sauce, white sugar and brown sugar with an electric mixer in a large bowl until smooth. Add the eggs one at a time, allowing each egg to blend into the butter mixture before adding the next. Beat in the vanilla with the last egg.
Beat in the flour mixture until just incorporated. Fold in the chocolate chips, grated chocolate and walnuts mixing just enough to evenly combine. Drop by rounded teaspoons onto ungreased baking trays.
Bake in the preheated oven until the edges are golden, 8 to 10 minutes. Allow the biscuits to cool on the baking tray for 1 minute before removing to a wire rack to cool completely.