In a medium bowl, whisk together gochujang, tamari, sesame oil, honey, ginger, and garlic to create the marinade.
Add the cubed pork tenderloin and pork belly to the bowl, tossing until every piece is thoroughly coated; let marinate for at least 20 minutes.
Preheat your grill or grill pan to medium-high heat.
Thread the marinated pork tenderloin, pork belly, bell peppers, and red onion onto skewers, alternating to distribute the flavors.
Season the skewers lightly with sea salt and black pepper.
Grill the skewers for 4-5 minutes per side, or until the pork is cooked through and the belly fat has rendered into a crispy texture.
Remove from heat and sprinkle with toasted sesame seeds before serving.