In a large bowl, combine the first six ingredients until crumbly; sprinkle 1 cup into a greased 13-in. x 9-in. baking pan (do not press). , Bake at 350° for 10 minutes. In a small heavy saucepan, cook and stir caramels and milk until caramels are melted. , Pour over crust. Top with chocolate chips and nuts. Sprinkle with remaining oat mixture. Bake at 350° for 10 minutes. Cool on a wire rack. Refrigerate until set.