01 - Preheat oven to 375°F and lightly grease a 9x13-inch baking dish.
02 - In a large skillet over medium heat, melt butter. Add onions, carrots, and celery, and cook for 5 to 6 minutes until softened.
03 - Sprinkle flour over vegetables and stir continuously for 1 minute to cook the flour.
04 - Gradually whisk in broth and milk, stirring until mixture thickens, about 3 to 4 minutes.
05 - Add garlic powder, thyme, black pepper, and salt, stirring to combine.
06 - Stir in cooked turkey and peas, mixing thoroughly; simmer for 2 minutes.
07 - Transfer turkey mixture evenly into the prepared baking dish.
08 - Sprinkle shredded cheddar cheese evenly over the turkey mixture.
09 - Combine breadcrumbs with melted butter and sprinkle evenly over the cheese layer.
10 - Bake uncovered for 25 to 30 minutes until golden brown and bubbling.
11 - Optionally garnish with chopped fresh parsley before serving hot.