Add flank steak, onion, broccoli, garlic paste, ginger paste, Thai sweet chilli, dark soy sauce, oyster sauce, hoisin sauce, rice wine vinegar, sesame oil, and chicken stock to slow cooker
Cook on slow cooker setting until steak is tender
Mix cornflour with water to create slurry and stir into slow cooker to thicken sauce
Season with black pepper to taste
Serve hot
