Preheat the oven to 190°C (375°F). Lightly grease a baking dish.
Cook the egg noodles or pasta in salted water according to the package instructions until just tender. Drain and set aside.
Melt the butter in a large skillet over medium heat.
Add the chopped onion and mushrooms. Cook for 4–5 minutes until softened.
Add the minced garlic and cook for another 30 seconds.
Stir in the cream of mushroom soup, milk, and sour cream until smooth.
Add salt, black pepper, oregano, and paprika. Stir well and simmer gently for 2–3 minutes.
Add the drained tuna, frozen peas, cooked noodles, cheddar cheese, and mozzarella cheese. Mix gently until everything is well combined.
Transfer the mixture to the prepared baking dish and spread it evenly.
In a small bowl, combine the breadcrumbs, Parmesan cheese, and melted butter.
Sprinkle the breadcrumb mixture evenly over the top of the casserole.
Bake for 20–25 minutes, until the casserole is hot and bubbling and the top is golden brown.
Remove from the oven and let it rest for 5 minutes.
Garnish with fresh parsley, if desired, and serve warm.