In a large skillet cook chicken and celery in hot oil over medium heat until chicken is brown, stirring to break up chicken as it cooks. Drain tomatoes, reserving liquid. Add half of the tomatoes, the cooked brown rice, chile pepper, Cajun seasoning, and salt to chicken mixture. Remove tops, membranes, and seeds from sweet peppers. Spoon chicken mixture into peppers. Pour reserved tomato liquid and the remaining tomatoes into the bottom of a 5- to 6-quart slow cooker. Place peppers, filled sides up, on top of tomatoes in cooker.