Bring a large pot of salted water to a boil. Cook the egg noodles according to package directions until al dente. Drain thoroughly and set aside.
Meanwhile, lightly season the beef pieces with salt and pepper. Heat the vegetable oil in a large nonstick skillet or Dutch oven over medium heat. Once hot, sear the beef until browned on all sides. Transfer the meat to a large bowl, cover, and keep warm.
In the same pan, increase the heat to medium-high and melt the butter. Add the diced onion and sliced mushrooms, sautéing for about 5 minutes until the onions soften and the mushrooms turn golden. Sprinkle in the remaining salt, pepper, and oregano. Reduce the heat to low and stir in the minced garlic, cooking for 20 seconds until fragrant. Transfer this mixture to the bowl with the beef. Cover to retain warmth.
Pour the beef broth and Worcestershire sauce into the skillet, scraping the browned bits from the pan’s surface. Bring to a gentle simmer.
In a small bowl, whisk together the cornstarch and cold water until smooth. Add the slurry to the skillet, whisking continuously until the sauce thickens.
Return the beef, mushroom-onion mixture, and cooked noodles to the skillet. Toss to coat evenly in the gravy and heat through.
Serve hot, garnished with freshly chopped parsley.