Shred cabbage, placing half of it in a bowl. Reserve the other half. Sprinkle chopped onion over cabbage. Sprinkle chopped green pepper over onion. Top with remaining cabbage. Sprinkle sugar over the top of cabbage. Do not stir.
Bring oil, vinegar, salt and celery seed to a full boil, and pour this hot mixture over the cabbage mixture. Do not stir! Cover container, and place in refrigerator overnight.
Next day, stir well. This will keep for 10 days or longer in the refrigerator.