Boil a pot of water and cook the egg noodles according to package instructions until al dente, then drain and set aside.
Slice the lean sirloin steak into thin 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 steak strips until browned, about 2 minutes per side.
Remove the steak from the skillet and set aside on a plate.
In the same skillet, add the sliced mushrooms and diced onions, sautéing until the onions are translucent and the mushrooms have released their moisture.
Add the minced garlic to the skillet and cook for 30 seconds until fragrant.
Pour in the beef broth to deglaze the pan, using a wooden spoon to scrape up any flavorful browned bits from the bottom.
Whisk in the Dijon mustard and Worcestershire sauce, then simmer for 3 minutes to allow the liquid to reduce slightly.
Reduce the heat to low and stir in the Greek yogurt until the sauce is smooth and creamy.
Add the cooked steak strips back into the skillet, tossing them gently to coat in the sauce.
Serve the beef and mushroom mixture over the prepared egg noodles and garnish with freshly chopped parsley.