Cook the egg noodles in a large pot of boiling water until al dente, then drain and set aside.
Season the sliced beef sirloin evenly with the sea salt and black pepper.
Heat the olive oil in a large skillet over medium-high heat until shimmering.
Add the beef to the skillet in a single layer and sear until browned, about 2 minutes, then transfer to a plate.
In the same skillet, add the sliced mushrooms and diced onion, sautéing until the mushrooms are golden and the moisture has evaporated.
Stir in the minced garlic and cook for 30 seconds until fragrant.
Pour in the beef bone broth to deglaze the pan, using a wooden spoon to scrape up any flavorful browned bits.
Whisk in the Dijon mustard and Worcestershire sauce, then let the liquid simmer for 3-4 minutes to reduce slightly.
Reduce the heat to low and stir in the plain Greek yogurt until the sauce is smooth and creamy.
Return the beef and cooked noodles to the skillet, tossing gently to coat everything in the sauce, and garnish with fresh parsley.