Preheat oven to 350°F/177℃. Spray a 9x13-inch baking dish lightly with nonstick cooking spray. Set aside.
Cook the noodles by the instructions on the package to al dente. Drain noodles and set aside. Drain tuna, flake it, and set aside.
Make breadcrumb topping by thoroughly mixing breadcrumbs, melted butter, and chopped parsley in a small bowl. Set aside.
Add oil to a large Dutch oven skillet over medium-high heat, then melt the butter. When it has completely melted, add onion, celery, carrots, garlic, and Italian seasoning. Saute for 4-5 minutes or until the onion is translucent and the vegetables are slightly cooked.
Sprinkle flour over the top of the vegetables and stir until thoroughly combined. Continue cooking for 1-2 minutes to remove the taste of raw flour.
Lower the heat to a minimum, and whisk in the milk. Continue stirring until the sauce thickens enough to coat the back of a spoon, 3-5 minutes.
Stir in the cheddar cheese (reserving a handful for topping). Mix using a wooden spoon until completely melted.
Add drained egg noodles, tuna, and peas to the cheese sauce. Mix thoroughly, and adjust the seasoning with salt and pepper to taste.
Transfer the tuna casserole to your prepared baking dish, and sprinkle the reserved cheese and breadcrumb topping evenly over the top.
Bake in a preheated oven until heated through and bubbly, 20-30 minutes.
When ready, remove from the oven, sprinkle with chopped fresh parsley, and enjoy.