In a mixing bowl, combine ground beef, breadcrumbs, egg, chopped onion, minced garlic, 1 teaspoon Worcestershire sauce, salt, black pepper, and dried parsley. Mix until well combined but do not overmix.
Roll the mixture into meatballs, about 1 to 1.5 inches in diameter. You should get about 18-20 meatballs.
In a large skillet over medium heat, lightly brown the meatballs on all sides (about 5-7 minutes). This step is optional but adds extra flavor.
Place the browned meatballs in the slow cooker.
In a separate bowl, whisk together cream of mushroom soup, beef broth, 2 tablespoon Worcestershire sauce, onion powder, garlic powder, and black pepper until smooth. Pour the gravy mixture over the meatballs in the slow cooker.
Cover and cook on low for 6 hours, or until meatballs are cooked through and tender.
If desired, garnish with chopped fresh parsley before serving.