Cook the egg noodles according to package instructions until al dente, then drain.
In a large skillet over medium heat, heat the olive oil and sauté the chopped onion until golden brown.
In a large mixing bowl, combine the cooked noodles, shredded roast beef, cream of mushroom soup, sour cream, sautéed onion, Worcestershire sauce, salt, and pepper.
Transfer the mixture to a greased 9x13 inch baking dish and sprinkle shredded cheddar cheese on top.
Bake in the preheated oven for 25 to 30 minutes, or until the casserole is bubbly and the cheese is melted.
Let cool for a few minutes before serving.
Notes
This casserole is great for a family dinner or a potluck, and leftovers can be stored in the refrigerator for up to 3 days.