Preheat the oven to 425°F and prepare the crumb topping by mixing panko bread crumbs, melted butter, shredded cheddar cheese, and parsley; set aside. Boil egg noodles according to package instructions until al dente, drain, and rinse under cold water. In a skillet, sauté the diced onion and celery in butter until they become tender, about 5–7 minutes. In a large mixing bowl, combine the cooked noodles, sautéed vegetables, thawed peas, condensed soup, milk, shredded cheddar cheese, drained tuna, and parsley; stir thoroughly to incorporate. Evenly spread the mixture into a 2-quart baking dish and sprinkle the prepared crumb topping over the surface. Bake for 18–20 minutes until the casserole is hot and the topping is golden and bubbling.