Heat oven to 350 degrees. Grease 13x9-inch baking pan. Combine oats, flour, brown sugar, soda and salt; mix well. Stir in margarine, mixing well until blended. Reserve 1 cup; press remaining onto bottom of prepared pan. Bake 10 to dozen minutes or until light brown; cool 10 minutes. Top with nuts and chocolate pieces. Mix caramel topping and quarter cup flour until smooth; drizzle over chocolate pieces to within 1 cm of pan edges. Sprinkle with reserved oat mixture. Bake an additional 18 to 22 minutes or until golden brown. Cool; chill until set. Makes 32 bars.