In a small bowl, whisk together the gochujang, tamari, sesame oil, honey, rice vinegar, minced garlic, and grated ginger to create the marinade.
Cut the pork tenderloin and pork belly into 1-inch cubes, ensuring they are uniform for even cooking.
Thread the pork cubes onto skewers, alternating between the lean tenderloin and the rich pork belly pieces.
Brush the skewers generously with half of the gochujang marinade and let them marinate for 10 minutes.
Heat a grill pan or outdoor grill over medium-high heat and lightly coat with a touch of oil.
Grill the skewers for 3-4 minutes per side, brushing with the remaining marinade during the last few minutes of cooking until charred and cooked through.
Thinly slice the green onion and the cucumber.
Serve the skewers hot, garnished with sesame seeds and green onions, with the fresh cucumber slices on the side.