Cook the egg noodles according to package directions in salted water; drain and set aside.
Slice the beef sirloin into thin strips and season evenly with sea salt and black pepper.
Heat olive oil in a large skillet over medium-high heat and sear the beef strips until browned on all sides, then remove them from the pan and set aside.
In the same skillet, add the diced onion and sliced mushrooms, sautéing until the vegetables are tender and golden brown.
Add the minced garlic to the skillet and cook for 1 minute until fragrant.
Pour in the beef broth and Dijon mustard, using a wooden spoon to scrape up any browned bits from the bottom of the pan.
Reduce the heat to low, return the beef to the skillet, and stir in the Greek yogurt until the sauce is creamy and heated through without boiling.
Place the cooked egg noodles in a bowl, top with the beef and mushroom sauce, and garnish with chopped fresh parsley.