Soak four wooden skewers in water for at least 20 minutes to prevent burning.
Cut the pork tenderloin and pork belly into uniform 1-inch cubes.
In a small bowl, whisk together the gochujang, tamari, toasted sesame oil, rice vinegar, honey, minced garlic, and grated ginger to create a thick glaze.
Thread the pork tenderloin and pork belly onto the skewers, alternating the pieces to allow the pork belly fat to baste the lean tenderloin during cooking.
Brush the glaze generously over all sides of the skewers and let them marinate for 10 minutes.
Preheat a grill or cast-iron grill pan over medium-high heat and lightly grease with a high-smoke point oil if needed.
Place the skewers on the grill and cook for 3-4 minutes per side, or until the pork is cooked through and develops a charred, caramelized exterior.
While the pork cooks, slice the cucumber into thin rounds and toss with sea salt and black pepper.
Remove the skewers from the heat and let them rest for 2 minutes.
Serve the skewers over the seasoned cucumbers and garnish with a sprinkle of sesame seeds.