PREHEAT oven to 350°F. Grease bottom of 13×9-inch baking pan.
COMBINE oats, 1-1/2 cups flour, brown sugar, baking soda and salt in large bowl. Stir in butter; mix well. Reserve 1 cup oat mixture; press remaining oat mixture onto bottom of prepared baking pan.
BAKE for 12 to 15 minutes or until golden brown. Sprinkle with morsels and nuts. Mix caramel topping with remaining flour in small bowl; drizzle over morsels to within 1/4 inch of pan edges. Sprinkle with reserved oat mixture.
BAKE for 18 to 22 minutes or until golden brown. Cool in pan on wire rack; refrigerate until firm.