Heat both the olive oil and the sesame oil in a large saucepan. Add the pork belly and brown on each side for around 2 minutes. Pour in enough water to cover the pork and add the ginger. Bring it to the boil and then turn down the heat, cover and allow the pork to simmer for 1½ hours. Skim off any impurities that form on top of the surface during this time.
Remove the pork from the pot. Reserve 1 litre of the water the pork has simmered in and discarding the rest. Place the pork, the cooking liquid, dashi stock powder, sake, mirin, brown rice vinegar, honey and tamari in a clean saucepan and bring to the boil. Then turn down the heat and simmer uncovered for 1 hour, turning occasionally to ensure even cooking.
Remove the pork from the braising liquid and dice into bite size portions. Increase the heat of the braising liquid and cook until it is reduce by one third. Place the pork pieces back in the sauce and remove from the heat, allowing the pork to sit in the sauce for 15 minutes.
Serve the pork with cooked soba noodles and steamed greens.