Cut the pork belly and pork tenderloin into uniform 1-inch cubes.
In a medium-sized bowl, whisk together the gochujang, tamari, toasted sesame oil, minced garlic, and grated ginger to create the marinade.
Add the pork cubes to the bowl and toss until every piece is thoroughly coated; allow to marinate for at least 15 minutes.
While the pork is marinating, slice the zucchini and red bell pepper into 1-inch chunks suitable for skewering.
Thread the marinated pork, zucchini, and bell pepper onto skewers, alternating the ingredients for a balanced bite.
Preheat a grill pan or outdoor grill to medium-high heat and lightly coat with a high-heat cooking spray.
Place the skewers on the grill and cook for 3-4 minutes per side, rotating until the pork is cooked through and the edges are beautifully charred.
Remove the skewers from the heat and garnish with thinly sliced green onions before serving immediately.