1Heat oven to 350°F (325°F for dark or nonstick pan). Grease and lightly flour or spray 15x10x1-inch pan. Make cake batter as directed on box. Pour into pan.
2Bake 20 to 27 minutes or until toothpick inserted in center comes out clean. Cool completely, about 1 hour.
3Fold crushed cookies into frosting. Cut cake crosswise in half. Remove one cake half from pan, using wide spatula to lift cake; place on serving plate. Spread cake with half of the frosting mixture.
4Top with remaining half of cake; spread with remaining frosting mixture. Garnish with cookie pieces. Store loosely covered.