Preheat the oven to 425°F and coat a casserole dish with nonstick cooking spray.
Boil the egg noodles according to the package instructions until al dente. Drain and rinse under cold water.
In a saucepan over medium heat, melt the butter. Add the onion and celery and cook for about 5-7 minutes or until tender.
In a large bowl, add the noodles, onion mixture, peas, mushroom soup, milk, 1 cup of cheddar cheese, tuna and parsley. Mix to combine and set aside.
Make a crumb topping by mixing the panko crumbs with the melted butter and the rest of the cheddar cheese.
In the prepared casserole dish, spread the tuna mixture evenly and then top with the crumb topping.
Bake for 18-20 minutes or until bubbly. Serve, and enjoy!