Cut steak into thin bite-size slice. In a slow cooker, combine soy sauce, sugar, ginger and garlic. Add steak. Cover and cook on low for 7 to 9 hours or until meat is tender. Remove meat with a slotted spoon; set aside. Carefully pour liquid into a 2-cup measuring cup; skim fat. Add water to liquid to measure 1-1/2 cups. Pour into a large saucepan. Combine cornstarch and water until smooth; add to pan. Cook and stir until thick and bubbly, about 2 minutes. Add meat and heat through. Brush rolls with butter; broil 4 to 5 inches from the heat for 2 to 3 minutes or until lightly toasted. Fill with meat, pineapple and green onions.