Place soy sauce, brown sugar, garlic, ginger, and scallions in a large heavy-bottom pan and bring to a gentle boil.
When the mix comes to a boil, remove from the heat and add the pork. Cover and place in the oven for 2 hours.
Remove the lid and cook uncovered for an additional 45 minutes to 1 hour. The pork should be tender.
Remove the pork from the sauce, let cook slightly and slice thin.
Pickled cucumbers and onions
Place the granulated sugar, salt, rice wine vinegar, water, and chili paste in a small sauce pan over a medium heat and stir until the sugar dissolved.
Pour the mixture over the cucumber and red onions, and leave for 2 hours.
Assembly
Steam the bao Buns for 6 minutes or until they are fluffy and fully cooked.
Spread 1/2 tbsp. of hoisin sauce inside each steamed bun.
Place 2 each 1 oz slices of cooked pork into each steamed bun.
Garnish each steamed bun with 1 oz of the drained pickled cucumber and red onion.
Top each steamed bun with 2 sprigs of fresh cilantro.