Heat oven to 350°F. Grease 13x9-inch pan. In large bowl, combine brown sugar and margarine; beat until light and fluffy. Add egg; blend well.
Lightly spoon flour into measuring cup; level off. Add flour and oats; mix well. Press evenly in bottom of greased pan.
Bake at 350°F. for 15 to 18 minutes or until light golden brown.
Meanwhile, in medium saucepan, combine caramels and half-and-half; cook over low heat until caramels are melted and mixture is smooth, stirring occasionally.
Remove crust from oven. Pour caramel mixture over partially baked crust. Sprinkle with cashews and chocolate chunks.
Return to oven; bake an additional 8 to 10 minutes or until chocolate is softened and caramel just begins to bubble around edges. If desired, swirl softened chocolate chunks with knife. Cool 1 hour or until completely cooled. If desired, refrigerate bars to set chocolate. Cut into bars.