Place pork belly in a vacuum seal bag. Slather your desired sauce (Char Siu or Soy/Honey) on both sides of the pork belly. Seal the bag and prepare your sous vide machine to run at 158F for 16 hours. Make sure you have enough water in the pot, topping off as needed. When done, open bag, reserving the Char Siu sauce in the bag. Slice the pork belly into 1/4".
To make the slaw, mix the cucumber and the bell pepper in a bowl, and toss with seasoned rice vinegar. For the green onion, slice as thinly as possible at a steep angle. Fill a small bowl with ice water, and add the sliced green onion.
When ready to serve, add the pork belly to a frying pan, then turn on the heat to medium. The pork belly will slowly caramelize, and fat will render as it heats up with the pan. Cook until browned, about 2 minutes. Flip and brown other side.
Drain the green onion from the ice water. Assemble tacos with warmed flour tortillas, pork belly, slaw and curly, crunchy green onion.