Preheat oven to 375 degrees F (190 degrees C).

Place chicken in a large pot and cover with water; bring to a boil and cook until chicken is no longer pink in the center, about 5 minutes. Drain.

Heat olive oil in a large skillet over medium heat. Stir carrots, onion, and salt into hot skillet, cover the skillet, and cook, stirring occasionally, until onions are tender, 8 to 10 minutes. Stir Cajun seasoning into vegetables.

Sprinkle flour over vegetable mixture in the skillet; cook and stir until flour taste cooks off, about 1 minute. Gradually stir orange juice and broth, respectively, into vegetable mixture; bring to a boil.

Stir chicken, peas, 1/2 of the parsley, and dill into broth mixture; remove from heat and stir in buttermilk. Pour buttermilk mixture into a baking dish.

Bake in the preheated oven for 15 minutes. Stir corn flakes and remaining parsley together in a bowl. Sprinkle corn flake mixture over chicken mixture; bake until corn flakes are golden and casserole is bubbling, about 5 minutes more. Let rest 5 minutes.