Lightly grease a 13x9x2-inch pan. In a medium bowl, stir together flour, cinnamon, nutmeg and baking powder; set aside.
In a separate bowl, cream together butter, brown sugar and sugar until light and fluffy. Add egg and beat on low speed until blended. Add reserved dry ingredients and continue to beat on low speed until well blended.
Fold in oatmeal, butterscotch chips and walnuts. Spread dough into prepared pan and bake 20-25 minutes or until light brown. (Do not over bake.)