Heat oven to 350°F. Generously grease 10-inch ovenproof skillet with shortening. In large bowl, beat butter, brown sugar and granulated sugar with electric mixer on medium speed 2 minutes or until light and fluffy. Beat in egg and vanilla. On low speed, beat in flour, baking soda and salt until blended. Stir in oats, cranberries and chocolate. Press dough in bottom of skillet.