1. In a large bowl, combine cabbage, carrots, green pepper and onion.
2. Add sugar and toss to coat.
3. In a saucepan, combine vinegar, oil, salt, mustard, and celery seed.
4. Bring to a boil.
5. Pour over cabbage mixture and toss to coat.
6. Cover and refrigerate for at least 2 hours before serving.
7. Coleslaw may be frozen up to 3 months, remove from the freezer 2 hours before serving.