In a large mixing bowl, combine the ground meat, breadcrumbs, egg, chopped green onions, minced garlic, and grated ginger. Mix gently until evenly blended.

Roll the mixture into small meatballs, about 1 inch in diameter, and place them in a tray.

In a separate bowl, whisk together soy sauce, hoisin sauce, rice vinegar, brown sugar, minced garlic, grated ginger, and chili flakes if using.

Place all meatballs in the slow cooker and pour sauce over them, gently tossing to coat evenly.

Cover and cook on low for 4 to 6 hours, until tender and fully cooked.

Sprinkle toasted sesame seeds, extra green onions, and cilantro over the cooked meatballs before serving.

Serve meatballs over rice, quinoa, or noodles with steamed or stir-fried vegetables.