Preheat the Oven: Start by preheating your oven to 350°F (175°C).
Cook the Turkey: In a large skillet over medium heat, add the ground turkey. Season with garlic powder, onion powder, salt, and pepper. Cook until browned and no longer pink, about 5-7 minutes. Remove from heat and set aside.
Sauté the Vegetables: In the same skillet, add the diced celery and chopped onion. Sauté for about 5-7 minutes until softened and starting to caramelize. Remove from heat.
Combine Ingredients: In a large mixing bowl, combine the cooked turkey, sautéed vegetables, turkey broth, herbed stuffing mix, shredded cheddar cheese, thyme, sage, parsley, and beaten eggs. Mix until everything is thoroughly combined.
Prepare Casserole Dish: Grease a 9x13 inch casserole dish with cooking spray or butter. Transfer the stuffing mixture into the dish and spread it out evenly.
Make the Herb Crust: In a separate bowl, combine the panko breadcrumbs with melted butter and a pinch of salt and pepper. Mix well. Sprinkle this mixture evenly over the top of the stuffing mixture in the casserole dish.
Bake: Place the casserole in the preheated oven and bake for 30-35 minutes, or until the top is golden brown and crispy.
Garnish and Serve: Once baked, let it cool for 5-10 minutes. Garnish with additional fresh parsley before serving.