For the Bao Buns:

Combine flour, yeast, sugar, and salt in a large bowl. Gradually add warm water and oil, mixing until a shaggy dough forms. Knead on a lightly floured surface for 8-10 minutes until smooth and elastic. Place dough in a lightly oiled bowl, cover, and let rise in a warm place for 1-1.5 hours, or until doubled in size.

Punch down the dough. Knead in the baking powder for 1-2 minutes until fully incorporated. Divide dough into 12-14 equal pieces. Roll each piece into a ball.

Flatten each ball into an oval shape. Brush one side with a tiny bit of oil and fold in half, pressing gently. Place each shaped bun on a small square of parchment paper. Cover and let rise for another 20-30 minutes.

Prepare a steamer with water at a rolling boil. Place buns, with parchment paper, into the steamer basket, ensuring space between them. Steam for 8-10 minutes. Do not open the lid during steaming. Once done, turn off heat and let sit for 2 minutes before opening the lid to prevent shrinking.

For the Crispy Pork Belly:

Score the skin of the pork belly. Rub salt generously into the skin. In a bowl, mix soy sauce, hoisin, honey, rice vinegar, five-spice, minced garlic, grated ginger, and brown sugar to create the marinade.

Rub the marinade all over the meat side of the pork belly, avoiding the skin. Place pork belly, skin side up, on a rack in a roasting pan. Roast in a preheated oven at 180°C (350°F) for 1.5-2 hours, or until the meat is tender and the skin is crispy. Remove from oven and let rest for 10 minutes before slicing into thin strips.

Assembly:

Gently open a warm bao bun. Fill with a few slices of crispy pork belly. Garnish with julienned cucumber, sliced green onions, a drizzle of Sriracha mayo, and fresh cilantro. Serve immediately.