Grate the zest from 1 orange, then segment the flesh (see Here to help, p23). Juice the other orange. Mix the zest with half the juice, vinegar, honey and garlic, then set aside. For the dressing, whisk the remaining juice
with the mustard, 1 tbsp oil and seasoning.
Heat the remaining oil in a frying pan, add the pork, then brown on each side, about 5 mins in total. Add the balsamic mixture, season, then bring to the boil. Bubble for 5-6 mins, turning the pork, until tender.
Meanwhile, tip the watercress into a bowl, toss with the avocado, orange segments and dressing, then serve alongside the pork.