Heat oven to 350°F (180°C). In large bowl, break up cookie dough. Stir in oats and brown sugar until crumbly (if necessary, knead with hands); reserve 1/2 cup (125mL) mixture for topping. In ungreased 9x13-inch (23x33 cm) rectangular baking pan, press remaining mixture evenly to form crust. Bake 10 to 15 minutes or until light golden brown.