Put the onion, ginger, vinegar, star anise and cinnamon into a bowl and cover with clingfilm. Chill in the refrigerator overnight.
Preheat the slow cooker if necessary; see the manufacturer's instructions. Pour the boiling water over the teabags and leave to brew for 2–3 minutes, then squeeze out the bags and discard. Rinse the ribs with cold water, drain and put into the slow cooker pot with the spiced onion mix and the hot tea.
Cover with the lid and cook on high for 30 minutes. Reduce the heat and cook on low for 7½–9½ hours, or set to auto for 8–10 hours, until the meat is almost falling off the bones.
Lift the ribs out of the slow cooker pot and transfer to a foil-lined grill pan. Put 6 tablespoons of stock from the pot into a bowl and mix in the honey and soy sauce. Spoon over the ribs, then grill for 10–15 minutes, turning several times and spooning soy mixture over until browned and glazed. Serve with pickled cucumber (see below) and rice.