Bring a medium pot of salted water to a boil and cook the whole wheat egg noodles according to package directions until tender.
While the noodles cook, heat the olive oil in a large skillet over medium-high heat.
Add the lean ground beef to the skillet, breaking it into small pieces with a spatula, and cook until completely browned.
Stir in the sliced cremini mushrooms and diced yellow onion, sautéing for 5-6 minutes until the mushrooms have released their moisture and turned golden brown.
Add the minced garlic, sea salt, and black pepper, cooking for an additional 60 seconds until the garlic is fragrant.
Pour in the beef broth and whisk in the Dijon mustard, using a wooden spoon to scrape up any flavorful browned bits from the bottom of the pan.
Reduce the heat to low and let the sauce simmer gently for 3 minutes to allow the flavors to meld.
Remove the skillet from the heat and stir in the Greek yogurt until the sauce is smooth, creamy, and fully incorporated.
Drain the cooked noodles and add them directly into the skillet, tossing gently to ensure every noodle is coated in the mushroom beef sauce.
Garnish with freshly chopped parsley and serve immediately while hot.