Preheat oven to 250º.
Place bread cubes on a large baking sheet. Bake at 250º for 1 hour or until dry, tossing occasionally.
Increase oven temperature to 350º.
Melt butter in a large nonstick skillet over medium-high heat. Add the onion, mushrooms, and celery to pan, and sauté 5 minutes. Add apple and cranberries; sauté 5 minutes. Add chestnuts; sauté 1 minute. Remove from heat; stir in parsley, sage, and thyme.
Combine pumpkin and the next 4 ingredients (pumpkin through eggs) in a large bowl. Add bread and mushroom mixture; stir gently to combine. Spoon mixture into a 13 x 9-inch baking dish coated with cooking spray; cover with foil. Bake at 350º for 45 minutes; uncover and bake an additional 15 minutes or until the top is crisp.