1Heat oven to 350°F. Spray bottom of 13x9-inch pan with cooking spray.
2In large bowl, stir cookie mix, oil, water and egg until soft dough forms. Press dough in pan using floured fingers.
3Bake 12 to 15 minutes or until set. Immediately sprinkle marshmallows over crust; bake 1 to 2 minutes longer or until marshmallows begin to puff.
4In 4-quart saucepan, cook corn syrup, butter, vanilla and chips over low heat, stirring constantly, until chips are melted. Remove from heat; stir in cereal and nuts. Immediately spoon cereal mixture evenly over marshmallows. Refrigerate 30 minutes or until firm. For bars, cut into 9 rows by 4 rows.