In a small bowl, whisk together the gochujang, tamari, sesame oil, garlic powder, and grated ginger to create the marinade.
Cut the pork loin, pork belly, and red bell pepper into uniform 1-inch cubes.
Place the pork and peppers in a glass bowl, pour over the marinade, and toss to coat thoroughly; let sit for at least 15 minutes.
Thread the marinated pork and peppers onto wooden or metal skewers, alternating the lean loin with the rich belly for maximum flavor.
Preheat a grill or grill pan over medium-high heat and lightly oil the grates.
Grill the skewers for 3-4 minutes per side, turning occasionally, until the pork is cooked through and develops a charred, caramelized exterior.
Remove from heat and garnish with thinly sliced scallions, sea salt, and black pepper before serving.