Stir-Fried Pork with Carrots and Bok Choy

1 teaspoon salt

1/4 teaspoon fresh-ground black pepper

3 tablespoons cooking oil

1 1/2 teaspoons cornstarch

1 tablespoon water

1 onion , cut into thin slices

3 carrot s, cut into 2-inch-long slices about 1/2-inch wide and 1/2 pound bok choy , cut into 1-inch pieces (about 3 cups)

2 cloves garlic , minced

1/2 teaspoon celery seeds

1/2 cup canned low-sodium chicken broth or homemade stock

1/4 cup fresh orange juice