In a medium bowl, whisk together the gochujang, tamari, rice vinegar, sesame oil, honey, minced garlic, and grated ginger until smooth.
Pat the pork tenderloin dry with a paper towel and cut into 1-inch cubes, then season lightly with sea salt and black pepper.
Toss the pork cubes in the gochujang marinade until every piece is well-coated and let it marinate for at least 15 minutes.
While the pork marinates, chop the red bell pepper into 1-inch squares and slice the zucchini into half-inch thick rounds.
Thread the marinated pork, bell pepper, and zucchini onto skewers, alternating the ingredients to ensure even cooking.
Preheat a grill pan or outdoor grill to medium-high heat and lightly brush the grates with a high-smoke point oil.
Place the skewers on the grill and cook for 8 to 10 minutes, turning every few minutes, until the pork is cooked through and has a beautiful char.
Transfer the skewers to a serving plate and garnish with a sprinkle of sesame seeds and thinly sliced green onions.