Spray 13x9-inch pan with cooking spray. In large microwavable bowl, microwave margarine uncovered on High 30 to 45 seconds or until melted. Add marshmallows; toss until coated. Microwave on High 1 minute 15 seconds to 1 minute 45 seconds, stirring every 30 seconds, until mixture can be stirred smooth.
Stir in cereal and sunflower nuts until well blended. Press evenly in pan.
In small microwavable bowl, microwave chocolate chips and oil uncovered on High 45 to 60 seconds, stirring very 15 seconds until melted and smooth. Drizzle over bars.
Cool about 1 hour or until glaze is set. For bars, cut into 6 rows by 4 rows. Store loosely covered.