Soak wooden skewers in water for 20 minutes to prevent burning during the grilling process.
In a medium mixing bowl, whisk together the gochujang, tamari, toasted sesame oil, grated fresh ginger, minced garlic, and rice vinegar until smooth.
Cut the pork loin and pork belly into uniform 1-inch cubes to ensure even cooking.
Add the pork cubes to the marinade and toss thoroughly to coat each piece; let it marinate for at least 15 minutes.
Thread the pork loin and pork belly cubes onto the skewers, alternating the cuts to allow the pork belly fat to baste the leaner loin.
Preheat a grill pan or outdoor grill to medium-high heat and lightly grease the surface.
Grill the skewers for 3-4 minutes per side, turning occasionally, until the pork is cooked through and the edges are beautifully charred and caramelized.
Transfer the skewers to a serving plate and garnish with thinly sliced green onions and a sprinkle of sesame seeds.