With a sharp knife, cut slits in the surface of the chestnuts. Place chestnuts in a medium saucepan with enough water to cover, and bring to a boil. Cook 25 minutes, or until tender. Drain, peel, and chop.
Preheat oven to 350 degrees F (175 degrees C).
Melt margarine in a medium saucepan over medium heat. Stir in chestnuts, onion, salt, pepper, and poultry seasoning, and cook until onions are tender, about 3 minutes. Transfer to a medium baking dish, and mix with the cubed bread.
In a small bowl, beat together eggs and milk, and drizzle over the cubed bread mixture.
Bake 30 to 45 minutes in the preheated oven, until surface is crisp and lightly browned.