Heat oven to 350°F. Grease or lightly spray cookie sheet with nonstick cooking spray. In large bowl, break up cookie dough. Add oats and cinnamon; knead dough with clean hands until well mixed. Press dough into 10 x 14-inch rectangle (about 1/8-inch thick) on cookie sheet. Using a pizza cutter or thin-bladed knife, cut rectangle into 2-inch squares (Do not separate.) Using the dull side of a table knife, gently make tic-tac-toe grid on each cookie (Do not cut completely through cookies.) Bake 16 to 18 minutes or until edges are golden and middle is set but soft. Immediately, re-cut 2-inch squares, if necessary, and transfer cookies to wire rack. (If cookies begin to stick to cookie sheet, return to the oven for 1 to 2 minutes to soften.) Cool completely. Decorate cookies as desired with icings, candies or sprinkles.