Pat dry the lamb and season with salt. In a small bowl, combine the black pepper powder, white pepper powder, cinnamon powder, 7-spice powder, turmeric powder, orange zest and olive oil to make a smooth marinade paste, and generously rub it all over the lamb. Allow to rest for minimum 30 minutes.
Preheat the oven to 180 °C.
In a large cast iron pot, add a couple tablespoons of vegetable oil. Heat on medium fire and brown the lamb on all sides.
Remove the lamb and reserve on the side. In a large pot, add onions, carrots, celery, garlic bulbs, orange slices, thyme sprigs and bay leaves. Add the lamb and cover with chicken stock and water, and season with salt.
On the stove top, bring the liquid to a boil. Cover the pot with the lid and place in the oven pan, and braise for 4 hours.