In a medium bowl, whisk together the gochujang, tamari, toasted sesame oil, rice vinegar, minced garlic, and grated ginger to create the marinade.
Cut the pork tenderloin and pork belly into 1-inch cubes. Chop the red bell pepper into similar sized squares.
Toss the pork cubes and bell peppers in the marinade until every piece is thoroughly coated, then season with sea salt and black pepper.
Thread the pork and peppers onto skewers, alternating between the lean tenderloin, the rich pork belly, and the bell peppers.
Preheat a grill pan or outdoor grill to medium-high heat and lightly grease with a high-heat oil if necessary.
Grill the skewers for 3 to 4 minutes per side, or until the pork is cooked through and the edges are beautifully charred and caramelized.
Remove from heat and let rest for 2 minutes before serving hot.