Heat oven to 350'F. Lightly grease 23 cm square baking pan. In large bowl, combine oats, brown sugar and margarine; mix well. Spread into prepared pan. Bake 13 minutes or until light golden brown; cool on wire rack. In small saucepan over low heat, melt chocolate pieces. Spread over baked oat mixture; sprinkle with peanuts. Chill 4 hours or until chocolate is set. Cut into 2x 4 cm bars. Store tightly covered in refrigerator. Makes about 28 bars.