To prepare the meatloaf, spray a skillet with the nonstick cooking spray and heat over medium heat. Place the onion and celery on the pan and sauté about 5 minutes, stir often.
Mix the turkey, parsley, bread crumbs, milk, egg white, garlic, thyme, nutmeg, and 1/4 teaspoon of pepper in a bowl. Add the celery and onions once they are done cooking.
Shape into a loaf and put in a loaf pan that is coated with nonstick cooking spray. Place in the oven and bake for 50 minutes, or until the internal temperature reaches 165 degrees F.
To make the sauce, put the margarine in a saucepan and melt. Stir in the mushrooms and sauté until they are tender.
Remove from the heat and add the chicken broth, 1/8 teaspoon of nutmeg, 1/8 teaspoon of pepper, and 1/8 teaspoon of salt. Place back over the heat and cook for approximately 5 minutes, or until thickened and perfumed.
Once the meatloaf has cooked, unmold, slice, and separate onto plates. Pour the sauce over the turkey loaf and serve.