Soak wooden skewers in water for 20 minutes to prevent burning during the grilling process.
In a medium bowl, whisk together the gochujang, tamari, toasted sesame oil, rice vinegar, grated ginger, and minced garlic.
Cut the pork tenderloin and pork belly into one-inch cubes and add them to the bowl, tossing until every piece is thoroughly coated in the marinade.
Thread the marinated pork onto the skewers, alternating between the pork tenderloin, pork belly, red bell pepper chunks, and green onion pieces.
Season the assembled skewers lightly with sea salt and black pepper on all sides.
Preheat a grill or heavy grill pan over medium-high heat and lightly grease with a high-heat oil if necessary.
Grill the skewers for 3 to 4 minutes per side, turning occasionally, until the pork is cooked through and the edges develop a deep caramelized char.
Remove the skewers from the heat and let them rest for 2 minutes to allow the juices to redistribute before serving.