Turn your Instant Pot to sauté for 30-40 minutes. Season the pork belly generously with salt and pepper. When the Instant Pot reads Hot, add olive oil and sear the pork belly on all sides. You may need to do this in two batches. Set aside and put on a plate.
Add onions to the Instant Pot and sprinkle with a little salt and pepper, sauté for 2-3 minutes, stirring occasionally. Add garlic, herbs, star anise, cloves, cinnamon stick, peppercorns and sauté for 2-3 minutes. Add the pork belly back to the pot. Add rock sugar, Mirin and enough chicken stock to cover the pork belly. Be sure to not go over the max lines of your Instant Pot.
Once the sugar is mostly broke down. Turn off the sauté function and cover your Instant Pot. Set to pressure cook high for 20 minutes. Once complete, let it sit for an additional 10 more minutes before releasing the steam valve. If you want the meat to be a bit more tender, you can add more time.
Remove the pork and set aside in a large serving bowl. Set the pot on sauté for 20 minutes. Reduce the stock until the desired flavor is reached. Strain the sauce and skim the excess oil off the top or use a fat strainer. Add salt and pepper to taste. If you want to have a thicker sauce, mix 2 tbsps of cold water with 1 tsp of cornstarch and mix in after reducing. Cook for a couple more minutes and then pour over pork and serve with rice and cucumbers.