In a large bowl, beat brown sugar, granulated sugar, and butter with electric mixer until well combined.
Add eggs; beat well. Beat in peanut butter and vanilla until well combined. Beat in baking soda. By hand, stir in rolled oats, nuts, milk-chocolate pieces, and semisweet chocolate pieces.
Using 1/4 cup of dough for each cookie, drop cookies 3 inches apart onto ungreased cookie sheets. Flatten cookies slightly. Bake in a 350 degree F oven for 13 to 15 minutes or until edges are firm. Let cool on cookie sheets for 1 minute. Transfer cookies to wire racks; let them cool completely.
Decorate with Mint-Chocolate Drizzle and/or Candy Coating Drizzle. Makes 24 cookies.