Pre-heat the oven to 350° F.
Cube 1 whole loaf of bread and set aside.
Melt the butter in a skillet.
Sauté the celery, onion, and apples in the butter for about 5 minutes.
Mix the sautéed mixture with the cubed bread in a large bowl, making sure all of the bread is moistened.
Add sage, parsley, salt, and pepper to the mixture. Stir well.
Finally, add the walnuts to the mixture and mix well.
Spray a large 9x13 casserole dish with cooking spray.
Add the stuffing mixture to the dish.
Bake uncovered at 350° F for about 20 minutes.
Cover with foil and bake an additional 15 minutes.
Remove from the oven, and serve while warm.