Put the pork into a large plastic food bag or freezer bag and add the red food colouring, garlic, ginger, curry paste, soy sauce, sugar and sesame oil. Roll the mixture around to coat the pork, then seal the bag. Chill overnight, or for at least 8 hours.
Preheat the oven to Gas 5, 190°C, fan170°C. Put the pork in a foil-lined roasting tin. Roast, uncovered, for 15mins, then baste with the marinade. Cook for a further 20mins, basting after 10mins. Remove from the oven, cover with foil and rest for 10mins before slicing.
Heat the vegetable oil in a wok or large frying pan and add the mangetout, broccoli, pak choi, spring onions and chilli (if using). Stir-fry over a high heat for 4-5mins. Serve with the sliced pork and sprinkle with soy sauce.