When you make this recipe, make a double or triple batch so you can do the work once, fill a few casserole dishes, freeze and have homemade frozen dinners for multiple nights. Top them with a different topping each time and it will be like a whole new dinner.
Heat 2 tablespoons of EVOO in a large skillet over medium-high heat. Season the chicken chunks with salt and ground black pepper then sauté them on all sides in the hot pan until golden brown. Remove from skillet and reserve on a plate. (If using chopped rotisserie chicken, skip this step!)
Add the butter, onion, carrot, celery and garlic to the same skillet and cook, stirring occasionally, until the vegetables are tender, 5-6 minutes.
Sprinkle in the flour and cook until light brown, about 1 minute. Whisk the chicken stock into the veggie-butter-flour mixture and bring it to a boil. Simmer the gravy until thickened, 2-3 minutes, then return the browned chicken back to the pan and mix to combine.
Transfer everything to an 8 x 8" casserole dish and set aside until cool. Cover tightly with plastic wrap and freeze.
Cooking instructions: Take the casserole out of the freezer and top it with your favorite mashed potatoes, wild rice mixed with a half a cup of shredded cheddar cheese or a can of pop biscuits. Cover with foil and bake in a 400°F oven for an hour, remove the foil and bake another 20-30 minutes.