Add the beef stew meat, onion, carrots, and potatoes to the slow cooker.
Stir together the soy sauce, ground ginger, garlic powder, and beef broth in a bowl until combined.
Pour the liquid mixture over the meat and vegetables in the slow cooker.
Cover and cook on low for 8 hours.
In the final 30 minutes, mix the cornstarch with 2 tablespoons of water and stir it into the stew to thicken the sauce.
Sprinkle the green onions over the top just before serving.