Cut the pork fillet into large chunks, removing any excess fat. Fry in a heavy casserole dish or pan until browned. Add the onion until softened.
Mix the vinegar, sweet soya sauce, chilli and Chinese spice with the passata and vegetable stock. Pour all of this into the pork and onion mixture.
Cook on the stove top on low for about 40 mins until the pork is softened. Keep an eye on it to make sure it doesn't dry out. Add water if necessary.
Scatter the spring onions and sesame seeds over the pork. Serve with rice and asparagus tips lightly fried in butter.
