Preheat oven to 350°F. Spray 9x13 inch baking dish with cooking spray and set aside.

In large saucepan, heat butter over medium heat. Cook and stir chopped carrot and celery, onions, garlic, and poultry seasoning until tender. Stir in gravy. Bring to a boil. Stir in chicken and peas; season to taste with salt and pepper. Transfer to prepared baking dish and set aside.

For dumplings, in a medium bowl, stir together baking mix, buttermilk, and parsley until moistened. Drop by tablespoons onto casserole.

Bake, uncovered, for 25 minutes. Cover with foil and bake about 10 minutes more or until dumplings are cooked through. Serve hot.