Trim fat from steak. Cut beef diagonally across grain into thin slices. Set aside.
Heat a large nonstick skillet coated with cooking spray over medium-high heat. Add onion; sauté 6 minutes. Add mushrooms; sauté 4 minutes or until tender.
Combine flour and next 3 ingredients in a bowl. Add beef, tossing to coat. Heat oil in pan over high heat. Add beef; sauté 6 minutes or until beef is done. Add reserved onion mixture and broth. Bring to a boil, reduce heat, and simmer 2 minutes or until sauce is thick. Remove from heat; stir in sour cream. Sprinkle with parsley. Serve over noodles.
MyRecipes is working with Let's Move!, the Partnership for a Healthier America, and USDA's MyPlate to give anyone looking for healthier options access to a trove of recipes that will help them create healthy, tasty plates. For more information about creating a healthy plate, visit www.choosemyplate.gov.