Bring a small pot of water to a boil and cook the egg noodles according to package directions until al dente, then drain and set aside.
Slice the beef sirloin into thin strips and season 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 both sides, about 2 minutes, then remove from the pan and set aside.
In the same skillet, add the diced yellow onion and sliced mushrooms, sautéing until the onions are translucent and the mushrooms have released their moisture.
Stir in the minced garlic and cook for 30 seconds until fragrant.
Pour in the beef broth, Dijon mustard, and Worcestershire sauce, scraping the bottom of the pan to release any browned bits.
Reduce the heat to low and simmer the sauce for 3-5 minutes until slightly reduced.
Remove the skillet from the heat and stir in the Greek yogurt until the sauce is smooth and creamy.
Add the beef and cooked egg noodles back into the skillet, tossing gently to coat everything in the sauce.
Garnish with chopped fresh parsley and serve immediately.