Cut the pork tenderloin, pork belly, bell pepper, and zucchini into uniform 1-inch cubes.
In a medium bowl, whisk together the gochujang, tamari, toasted sesame oil, rice vinegar, grated ginger, and minced garlic to create the marinade.
Add the pork cubes to the bowl and toss until thoroughly coated; let marinate for at least 15 minutes.
Thread the marinated pork, bell peppers, and zucchini onto skewers, alternating between the ingredients.
Season the assembled skewers lightly with sea salt and black pepper.
Preheat a grill or grill pan over medium-high heat and lightly grease with a high-heat oil if necessary.
Grill the skewers for 3-4 minutes per side, or until the pork is cooked through and the edges are slightly charred.
Remove from heat and garnish with toasted sesame seeds and thinly sliced green onions before serving.