Preheat the oven to 350°F. In a large baking dish, combine the chopped onion, carrots, celery, wild rice, and chicken broth. Cover tightly with foil and bake for 1 hour and 15 minutes.
While the rice is cooking, melt 4 tablespoons of butter in a saucepan over medium heat. Add the flour, salt, and poultry seasoning. Cook for 1 minute until fragrant. Gradually whisk in the milk to form a smooth, creamy sauce.
Melt the remaining 6 tablespoons of butter. Toss with the cubed bread.
Once the rice is cooked, remove the foil. Add the raw chicken pieces and creamy sauce to the dish. Stir everything together to combine thoroughly. Arrange the buttered bread cubes evenly on top.
Increase the oven temperature to 450°F. Bake uncovered for an additional 20-30 minutes until the chicken is fully cooked and the bread cubes are golden brown.
Once baked, garnish with salt, pepper, or parsley and serve.