Creamy chicken with rice with back

1 tablespoon olive oil 1 cup carrot , peeled and chopped 1/2 cup celery , chopped 1/4 cup green onion , chopped (if making in the winter, you can substitute[...]

2 1/2 lbs chicken pieces (bone and skin in) 1 cup mayonnaise , tangy, not bland 4 tablespoons prepared mustard , preferably wholegrain and creamy 1 teaspoon[...]