Coat the bottom of a 6-quart or larger slow cooker with nonstick cooking spray. Add the sirloin steak and cover the meat with salt, pepper, dillweed, garlic powder and onion powder. Stir to coat evenly.
Add mushrooms, beef broth, worcestershire sauce and dijon mustard. Stir mixture well and cook on high for 2-3 hours or on low for 5-7 hours while stirring periodically.
When cook time is complete, stir in the corn starch. Mix well and cook on high for an additional 20 minutes. Next, add the greek yogurt. Mix well and cook on high for an additional 10 minutes.
While the stroganoff finishes cooking, begin to cook the noodles according to the package directions.
When both noodles and stroganoff are complete, add the noodles into the slow cooker, mix well and serve immediately. Garnish with fresh cut parsley or thyme.