MIX butter, brown sugar, corn syrup, vanilla and salt with electric mixer until smooth. Stir in oats. Press into greased 8 or 9-inch square pan.
BAKE at 350°F for 15 to 18 minutes or until center is barely firm. Cool on wire rack 5 minutes.
SPRINKLE with chocolate chips; top with small spoonfuls of peanut butter. Let stand 5 minutes; spread peanut butter and chocolate over bars, swirling to marbleize.
COOL completely on wire rack. Refrigerate 15 minutes to set topping. Cut into bars.