Cook the noodles – Boil the noodles in salted water until al dente. Drain and set aside.
Prepare the sauce – In a large bowl, combine the cream of mushroom soup, milk, sour cream, and seasonings. Whisk until smooth.
Combine the ingredients – Stir in the tuna, peas, onion, and cooked noodles. Mix well to evenly coat everything in the sauce.
Add cheese – Fold in half of the shredded cheddar cheese for creamy texture.
Transfer to baking dish – Pour the mixture into a greased 9×13-inch baking dish and spread it evenly.
Add topping – Mix breadcrumbs or crushed chips with melted butter, then sprinkle over the top of the casserole.
Bake until golden – Bake at 375°F (190°C) for 25–30 minutes until bubbly and lightly browned.
Cool and serve – Let it rest for a few minutes before serving for the best consistency.
