In a large mixing bowl beat the peanut butter and butter with an electric mixer on medium to high speed for 30 seconds. Add the brown sugar, granulated sugar, baking powder, and baking soda; beat until combined. Beat in the eggs and vanilla until combined. Stir in the rolled oats. Stir in the nuts and the candy-coated milk chocolate pieces.
Drop dough by 1/4-cup measure or scoop 4 inches apart onto parchment paper-lined cookie sheets. Bake cookies in a 350 degree F oven for about 15 minutes or until edges are lightly browned. (Or, for small cookies, drop dough by rounded teaspoons about 2 inches apart onto an ungreased cookie sheet. Bake cookies in a 350 degree F oven about 10 minutes or until edges are lightly browned.) Cool 3 minutes on the cookie sheet. Transfer cookies to wire racks; cool. Makes 26 cookies.