This Slow Cooker Salisbury Steak Meatballs recipe offers a hearty and comforting meal made easy with frozen meatballs simmered in a savory brown gravy enhanced with onion soup mix, ketchup, and Worcestershire sauce. Perfect for a hands-off dinner, these tender meatballs cook low and slow in the crockpot, then are thickened with a cornstarch slurry to create a rich gravy that pairs wonderfully with egg noodles or mashed potatoes.