In a large bowl, cream butter and brown sugar until light and fluffy. Beat in egg. Combine flour and oats; gradually add to creamed mixture.
Press into a 13 x 9 inch baking pan coated with cooking spray. Bake at 350 for 15-18 minutes or until golden brown.
Meanwhile, in a small saucepan, combine unwrapped caramels and cream. Cook over low heat for 4-5 minutes or until caramels are melted, stirring occasionally. Pour over crust. Sprinkle with the chocolate chunks and cashews.
Bake for 8-10 minutes or until chocolate is melted. Cool on a wire rack before cutting.