Bring a 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 half of the sea salt and black pepper.
Heat the olive oil in a large skillet over medium-high heat and sear the beef strips until browned, about 2 minutes per side, then remove from the pan.
In the same skillet, add the sliced cremini mushrooms and diced yellow onion, sautéing until the mushrooms are golden and the onions are soft.
Add the minced garlic and cook for 30 seconds until fragrant, then pour in the beef broth and Dijon mustard, scraping the bottom of the pan to release the flavor.
Reduce the heat to low and stir in the plain Greek yogurt until the sauce is smooth and creamy.
Add the beef and cooked noodles back into the skillet, tossing gently to coat everything in the sauce.
Season with the remaining salt and pepper, and garnish with freshly chopped parsley before serving.