Boil a pot of water and cook the egg noodles according to package directions until al dente; drain and set aside.
Thinly slice the sirloin steak into strips and season evenly with sea salt and black pepper.
Heat the olive oil in a large skillet over medium-high heat and sear the beef strips until browned on all sides, then remove from the pan and set aside.
In the same skillet, add the sliced mushrooms and diced onions, sautéing until the vegetables are softened and golden brown.
Stir in the minced garlic and cook for 30 seconds until fragrant.
Pour in the beef broth, Dijon mustard, and Worcestershire sauce, using a wooden spoon to scrape the bottom of the pan to release the flavorful browned bits.
Lower the heat to a simmer and return the beef to the skillet, cooking for 2-3 minutes until the sauce slightly reduces.
Remove the skillet from the heat and stir in the Greek yogurt until the sauce is creamy and fully incorporated.
Serve the beef and mushroom mixture over the cooked egg noodles and garnish with freshly chopped parsley.