Bring a large pot of water to a rolling boil over high heat. Add the pork belly, ginger, garlic, and white parts of the scallions. Boil for 30 minutes.

In a deep skillet, heat grapeseed oil over medium heat. Sauté the ginger, garlic, and white scallion parts for about 1 minute.

Stir in the star anise and cinnamon stick, then pour in the regular soy sauce, dark soy sauce, rice wine, brown sugar, and water, bringing the mixture to a vigorous boil.

Carefully arrange the cooked pork belly slices in a heat-proof dish that fits your steamer. Pour the braising liquid over the pork, ensuring it's well-covered.

Seal the dish with parchment paper and place it into a steamer over simmering water. Steam for 1.5 hours.

After steaming, allow the pork belly to cool for about 15 minutes. Once cool, slice into thick pieces.

Skim off any solidified fat from the surface of the pork belly and arrange slices inside soft buns. Garnish with the green parts of scallions.