First, you are going to dice the onion, green pepper, and celery. In a large skillet, over medium heat, combine the turkey, onion, green pepper, and celery. Cook until the turkey is brown and there is no pink. Drain the mixture when it's done cooking. In your slow cooker, pour the soup, ketchup, mustard, brown sugar, and pepper. Mix until well combined.Add in the turkey mixture and stir well. Turn the slow cooker to low and let cook for about 4 hours. When it's done, stir it well and take a little taste. This is when you can add the Worchester sauce if you want. Start with a little, stir, and taste again. A tip for easy cleanup - use a slow cooker liner. Those are my go-to whenever I do anything in the slow cooker. This recipe works best in a 3-quart slow cooker. But if you double or triple it use a 6-quart. I had tripled the recipe and used a 6-quart slow cooker. Leftovers are great! These reheat very well. Just heat the sloppy joe mixture in a bowl and then place in the bun.