In a spacious mixing bowl, combine the ground beef, breadcrumbs, finely chopped onion, chopped parsley, egg, garlic powder, salt, and pepper. Use your hands or a spatula to mix until all ingredients are well incorporated but do not overmix.
Shape the mixture into small meatballs, approximately 1 inch in diameter. You should yield about 20 to 25 meatballs.
In a separate bowl, whisk together the cranberry sauce, soy sauce, Dijon mustard, brown sugar, and apple cider vinegar until the mixture is smooth and homogeneous.
Arrange the meatballs in the slow cooker and gently pour the cranberry sauce mixture over them, ensuring each meatball is thoroughly coated in the sauce.
Secure the lid on the slow cooker and set it to cook on low for 4 to 6 hours, or on high for 2 to 3 hours, until the meatballs are cooked through and tender.
Once cooking is complete, carefully stir the meatballs in the sauce to ensure they are evenly coated before serving.
Notes
Serve over rice or mashed potatoes and garnish with fresh parsley.