Place the beef stew meat, mushrooms, and diced onion into the slow cooker.
Add the beef broth, Worcestershire sauce, garlic powder, paprika, salt, and black pepper. Stir to combine.
Cover and cook on low for 7 hours until the beef is tender.
In a small bowl, mix the cornstarch with 2 tablespoons of water until smooth. Stir the mixture into the slow cooker.
Cover and cook on high for 30 minutes to thicken the sauce.
Turn off the heat and let the mixture sit for 5 minutes before stirring in the Greek yogurt.
Meanwhile, cook the egg noodles according to package directions. Drain and divide among four bowls.
Spoon the beef and mushroom mixture over the noodles and sprinkle with chopped parsley.