The day before you want to cook the ribs, take a dish large enough to rest them snugly together in a single layer and pour in the soy sauce. Add the brown sugar, ginger, garlic, star anise and crushed peppercorns, stirring well to mix. Add the ribs and turn over a few times to make sure they are well coated then turn them all so they are meaty side down. Cover and refrigerate for 12-24 hours.
When you are ready to cook, fire up your barbecue and get it ready for indirect grilling - this means you can cook more slowly and gently. Use a chimney starter to light your coals and tip them into one side of your grill only, leaving the other side bare. For an extra smoky flavour add a couple of chunks of smoking wood to the fire. If you are using a kamado-style cooker, fire it up and get it running at around 125°C, again adding some smoking wood if you like.
Add the ribs meaty side up, along with the marinade leftover, to a sturdy roasting tin so they fit in a single layer, again so they are quite close together. Add a little cold water to the tin, so there is about 1cm of liquid in the bottom. This will help keep everything moist as it cooks and create a lovely spicy gravy.
Rest the tray of ribs on the grill bars on the opposite side of the fire and shut the lid. Leave to cook for about 4 hours, until they pull-apart tender. Every 30 minutes or so, use a spoon to pour a little of the cooking liquid over the ribs to baste as they cook. Halfway through cooking you can turn the ribs over so they are meaty side down - the meat will have absorbed all the smoke it's going to absorb by this time. Depending on the type of barbecue and charcoal you are using, you may need to add a little more fuel from time to time during the long slow cook. Once the ribs are cooked, remove the tin and cover with foil.
To grill the pak choi, add a little more fuel to the fire to get it good and hot. If you are using a big green egg-style cooker you can simply open the vents right up to raise the temperature. Drizzle the sesame oil over the pak choi and lay onto the grill bars above the fire so you can cook directly. Grill for a few minutes on each side until lightly charred but still with plenty of crunch.
To serve, pile the pak choi onto a serving plate. Add the ribs, along with a little of the sauce in the tin and sprinkle over the spring onion and chilli. Serve the rest of the sauce alongside.