Is there any low-calorie chocolate spread?

Our grown son who has down syndrome has become very heavy. He lives in a community residential setting. He loves Pop tarts chocolate flavor and has been allowed one each evening and one at his day program as reinforcement for good behavior. I have found more healthy alternatives to Pop tarts but they still are high in calories and fat. A dietitian suggested graham crackers. Is there any low calorie chocolate spread that could make these seem more like pop tarts?