Lay a large sheet of aluminum foil on a flat work surface. Lay 1/2 the green parts of the green onions down in the center of the foil. Place pork belly, fattiest-side down, on top of the green onions and top pork belly with remaining 1/2 the green parts of the green onions; sprinkle with salt. Fold aluminum foil tightly around pork and green onions. Wrap pork belly again in another sheet of aluminum foil. Place wrapped pork, seam-side up, in a loaf pan.
Cook pork belly in preheated oven for 5 1/2 hours. Turn off the oven heat and let cool in the oven for 2 hours. Remove from oven and chill in the refrigerator for 8 hours to overnight.
Remove pork from foil and discard green onions. Cut pork into 8 pieces.
Cook bacon in a skillet over medium heat until crisp all over, 2 to 4 minutes per side.
Whisk brown sugar, rice vinegar, fish sauce, ginger juice, and soy sauce together in a bowl.
Remove most of the fat from the skillet and discard. Add 1 tablespoon of the brown sugar glaze and increase heat to medium-high. Cook until pork is glazed on all sides and pieces are caramelized, about 10 minutes. Make a well in the center of the skillet and add chopped white parts of the green onion, garlic, and peppers. Saute until fragrant, about 1 minute.
Pour water and remaining brown sugar glaze into skillet; simmer until sauce thickens, 3 to 5 minutes.
