Heat sunflower oil in a large frying pan over medium heat.
Fry onions for 8 to 10 minutes until softened and lightly browned.
Add ginger, garlic, and chilli flakes, then cook for 3 minutes.
Season beef with pepper and coat with five-spice powder.
Add beef to the pan and fry for 4 minutes until browned.
Transfer ingredients to the slow-cooker and stir in stock and soy sauce.
Cover and cook on high for 4 hours until the beef is tender.
Whisk cornflour with 15ml water and honey to create a paste.
Stir the paste into the slow-cooker and cook for 15 minutes to thicken.
Serve beef with steamed rice or boiled noodles.