Soak wooden skewers in water for at least 20 minutes to prevent them from burning on the grill.
Cut the pork tenderloin and pork belly into uniform 1-inch cubes to ensure even cooking.
In a medium mixing bowl, whisk together the gochujang, tamari, rice vinegar, sesame oil, honey, grated fresh ginger, and minced garlic.
Add the pork cubes to the bowl and toss until every piece is thoroughly coated in the marinade, then let it rest for 15 minutes.
Thread the marinated pork and cubed red bell pepper onto the skewers, alternating the lean tenderloin with the fatty pork belly for optimal flavor.
Preheat a grill or cast-iron grill pan over medium-high heat and lightly coat with a high-smoke-point oil.
Place skewers on the grill and cook for 3-4 minutes per side, brushing with any leftover marinade, until the pork is cooked through and caramelized.
Remove from the heat and garnish with thinly sliced green onions and toasted sesame seeds before serving.