01 - Preheat oven to 375°F. Grease a 9 x 13-inch baking dish.
02 - Cook egg noodles according to package instructions until just al dente. Drain and set aside.
03 - Melt 2 tablespoons of butter in a large skillet over medium heat. Add diced onion, carrots, and celery; sauté for 5 to 6 minutes until tender.
04 - Sprinkle flour over vegetables and stir for 1 minute. Gradually whisk in chicken broth and milk, cooking until sauce thickens, about 4 to 5 minutes.
05 - Stir in garlic powder, thyme, salt, and pepper. Incorporate shredded chicken and frozen peas; remove from heat.
06 - Mix cooked noodles with sauce mixture thoroughly, then transfer to prepared baking dish.
07 - Combine panko breadcrumbs, grated Parmesan, melted butter, and chopped parsley in a bowl. Evenly sprinkle over noodle mixture.
08 - Bake uncovered for 25 to 30 minutes until bubbling and topping is golden brown.
09 - Allow casserole to stand for 5 minutes before serving.