Bring a pot of salted water to a boil and cook the egg noodles according to package directions until al dente, then drain and set aside.
Season the thinly sliced sirloin 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 quickly until browned, then remove from the pan and set aside.
In the same skillet, add the sliced mushrooms and diced onions, sautéing until the mushrooms are golden and the onions are translucent.
Stir in the minced garlic and cook for 30 seconds until fragrant.
Whisk the arrowroot powder and Dijon mustard into the beef broth, then pour the mixture into the skillet, scraping up any browned bits from the bottom.
Simmer the sauce for 2-3 minutes until it begins to thicken slightly.
Reduce the heat to low and stir in the Greek yogurt until the sauce is smooth and creamy, being careful not to let it boil.
Return the beef and any accumulated juices to the skillet, tossing to coat in the sauce and heating through.
Serve the beef and mushroom mixture over the cooked egg noodles and garnish with fresh chopped parsley.