Heat the vegetable oil in a frying pan and cook the onions over a medium heat until soft and translucent, about 5 minutes. Once cooked take off the heat, add the soy sauce and cool
In a large bowl add the beef, cooled onions, Chinese five-spice, bicarbonate of soda and salt and pepper. Mix well and then divide into 16 meatballs. Chill for 2 hrs in the fridge.
Preheat the oven to 180°C. In a large frying pan spray liberally with the sunflower oil and add the meatballs. turning occasionally ensure browned all over, about 5/6 minutes. Transfer to a baking tray and cook in the oven for 10 minutes.
While the meatballs are cooking, heat a wok to high heat. Add the seasme oil, red onion and carrots cooking for 2 minutes. Add the garlic and ginger and cook for a further 2 minutes. Next add the peppers and cook for 4 minutes.
Add the mushrooms, the meatballs and half the beef stock. Follow up with the hoisin sauce and rice wine vinegar, stir and bring to a simmer.
Mix the cornflour with a little water to make a paste then add this to the pan with the remaining beef stock. Add the mangetout and spring onions and cook for about 4-5 minutes until the just cooked, meatballs heated through and glossy.
Place in warmed bowls and serve.