In a large mixing bowl, combine the ground beef, breadcrumbs, chopped onion, egg, minced garlic, Worcestershire sauce, thyme, salt, and pepper. Mix until all ingredients are well incorporated.
Form the mixture into approximately 12 meatballs, about 1.5 inches in diameter.
Place the meatballs into the slow cooker.
In a separate bowl, whisk together the beef broth, ketchup, and soy sauce until smooth; pour this sauce over the meatballs in the slow cooker.
Cover and cook on low for 6-8 hours or on high for 3-4 hours, until the meatballs are cooked through and tender.
Once finished, mix the cornstarch and water in a small bowl to create a slurry. Stir this mixture into the slow cooker, and allow to cook for an additional 30 minutes on high until the sauce is thickened.
Taste and adjust seasoning if necessary.
Serve the Salisbury steak meatballs over mashed potatoes or rice, garnished with fresh parsley.
Notes
Serve over mashed potatoes or rice for a complete meal.