Add the oxtail to a large pot and fill it with water until it covers the oxtail. Bring the pot to a boil and let it parboil for 30 minutes.
Drain the pot and rinse the oxtail with water. Clean the pot and add back in the oxtail.
Fill the pot back with water until there is an inch above the oxtail. Add in the star anise, ginger, dried orange peel, and salt. Bring it to a boil then reduce it to a simmer. Cover and let it simmer for an hour.
Add in the peanuts and cover and simmer again for another 2-3 hours.
Oxtail should be tender enough to fall off of the bone. Add in the kai choy and let it cook for 10 minutes until it is tender (it is optional to take out the kai choy because it is bitter). Serve in a bowl, garnish with cilantro and green onions and enjoy!