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, sesame oil, honey, minced garlic, and grated ginger.
Place the pork cubes in a bowl and coat thoroughly with the gochujang marinade, letting it sit for 15 minutes.
Thread the pork onto the skewers, alternating between the lean tenderloin and the fatty pork belly pieces.
Preheat a grill or grill pan to medium-high heat and lightly grease.
Grill the skewers for 3-4 minutes per side, or until the pork is cooked through and the edges are slightly charred.
While the pork cooks, thinly slice the cucumber and toss with rice vinegar and red pepper flakes.
Remove skewers from the heat, sprinkle with sesame seeds, and serve immediately alongside the chilled cucumber salad.