Preheat oven to 375°F. Heat half the required vegetable oil in a large pot over medium-high heat. When the pot and oil are hot, add mushrooms and squash. Cook for about three minutes, allowing the vegetables to brown on all sides. Add remaining vegetable oil, chicken, onion, celery, garlic and salt; continue to cook for another three minutes. Add mushroom soup and chicken broth and stir well to combine. Continue cooking for about five minutes. Then add sage, nutmeg and walnuts. Stir to combine. When thoroughly mixed, remove from heat.

Place the dried bread in a large bowl and pour the warm stock over it. With a spoon, stir well until the bread is moist. Evenly spread the mixture in a greased 10 x 15-inch dish or similar sized bake-safe dish. Bake in oven for about 20 to 30 minutes, allowing the top to brown. Serve warm.