Spray inside of slow cooker with nonstick cooking spray.
Layer chopped potatoes, carrots, and onions in slow cooker.
Evenly place frozen meatballs on top of veggies.
In a medium size mixing bowl whisk beef broth, tomato paste, bouillon cubes, onion soup mix, salt, pepper, and garlic powder until combined. Pour over meatballs.
Cover and cook on low for 6-8 hours, or high for 4-5 hours or until potatoes and carrots can be pierced with a fork. Be careful not to overcook or potatoes will be mushy.
Once cooked, removed meatballs and set aside.
In a cup whisk cornstarch and cold water until smooth.
Pour cornstarch slurry into slow cooker and stir until slightly thickened.
Add meatballs back to slow cooker and stir well to coat meatballs.
Serve immediately with chopped parsley if desired.