In a large bowl, combine the ground beef, breadcrumbs, parmesan cheese, egg, salt, and pepper. Mix well to fully incorporate all ingredients.
Shape the mixture into about 20-25 meatballs.
In a separate bowl, whisk together the ketchup, brown sugar, apple cider vinegar, Worcestershire sauce, dijon mustard, garlic powder, and onion powder.
Pour the sauce into a slow cooker. Add the meatballs, making sure they are evenly distributed and covered in sauce.
Cover the slow cooker and cook on low heat for 4-5 hours, or until the meatballs are fully cooked and tender.
In a small bowl, whisk together the cornstarch and water. Stir the mixture into the slow cooker.
Cover and cook on high heat for an additional 15-20 minutes, or until the sauce has thickened.
Serve the meatballs hot with additional sauce on top, if desired. Enjoy!