Shred the meat and place in a wide pan. Pour in the chicken stock and add the oil, five spice, sugar and soy. Finely grate in the garlic and ginger, and season well.
Place on a high heat, bring to the boil, then reduce the heat a little and cook for 15 minutes, uncovered. You want most of the stock to have cooked away, with the meat coated in a rich, sticky glaze.
Meanwhile, make the rest of the filling. Peel and slice the carrots into matchsticks – use a julienne peeler if you have one. Prepare the cucumber in the same way, discarding the centre.
Trim and shred the spring onions. Place in a small bowl with the coriander and mint, squeeze over the juice of both limes, toss and sprinkle over the sesame seeds.
When you are ready to serve, warm up the bao buns according to their instructions. Place in a pile next to the pan of glazed meat, the shredded slaw and sriracha, and let everyone build their own.