Add the oil to a large non-stick pan, season the steaks well, then fry for 5 mins on each side until golden and almost cooked through. Mix the sugar, soy, tomato purée and most of the pineapple juice in a bowl.
Add the pineapple rings to the pan and let them caramelise a little alongside the pork. Add the chilli and five-spice to the pan, then fry for 1 min until aromatic. Tip in the soy mix and let it bubble around the pork and pineapple for a few mins until slightly reduced and sticky. Sprinkle with coriander, and serve with rice and Chinese greens.