Preheat Your Oven: Start by preheating your oven to 375°F (190°C). Lightly grease a baking dish with olive oil or cooking spray.
Sauté the Vegetables: Heat a drizzle of olive oil in a skillet over medium heat. Add the carrots, celery, and mushrooms, cooking for 5-7 minutes until softened. Season with garlic powder, salt, and pepper.
Prepare the Sauce: In a saucepan, melt the butter over medium heat. Stir in the flour and cook for 1-2 minutes to form a roux. Slowly add the broth, whisking to avoid lumps. Stir in the milk, thyme, and Parmesan. Cook until thickened, then season to taste.
Combine Everything: In a large bowl, mix the turkey, cooked wild rice, sautéed vegetables, and parsley. Pour the sauce over the mixture and stir well. Transfer to the baking dish.
Bake to Perfection: Bake for 20-25 minutes or until bubbly and golden on top. Garnish with extra parsley before serving.