Preheat oven to 350 degrees F. Spray a 9x13 inch casserole dish with cooking spray.
Heat a saute pan over medium high heat and add 1 tablespoon of oil. Add diced onions, carrots, and celery to the pan and saute for 4-5 minutes or until the veggies begin to soften. Add mushrooms and garlic and saute for another few minutes. Add veggies to the prepared casserole dish.
Add the wild rice and chicken broth. Cover dish tightly with foil and bake for 1 hour and 15 minutes.
When the rice is almost done cooking, melt 4 tablespoons of butter in a saucepan. Add flour, salt and poultry seasoning; let cook for 1 minute. Add the milk and 1/2 cup Parmesan cheese; cook and stir until thickened. Remove from heat.
Melt the other 4 tablespoons of butter and toss with the bread cubes.
When the rice is done cooking, remove pan from the oven. Add the chopped chicken and sauce; stir to combine. Add the bread cubes to the top and sprinkle with the remaining Parmesan cheese.
Increase the oven temperature to 400 degrees F. Return pan to the oven (uncovered) and bake for 15-20 minutes. Serve warm and enjoy!