Beef and Cabbage Sloppy Joes

1 lb ground beef

1/2 C onion, chopped

1/2 C celery, thinly sliced

2 C cabbage, shredded

1/3 C green pepper, chopped

3/4 C ketchup

1/4 C water

1/4 tsp salt

1 T mustard; prepared

8 hamburger buns, split and toasted

Cook and stir the meat, onion, and celery in a large skillet until the meat is brown.  Drain off the excess fat.  Stir in the cabbage, green pepper, ketchup, water, salt, and mustard and heat to boiling, stirring occasionally.  Reduce the heat and cover.  Simmer until the vegetables are tender, about 25 minutes.  Spoon the mixture onto the bottom halves of the buns and top with the remaining halves.