Prepare the marinade by combining soy sauce, banana ketchup, minced garlic, lemon juice, onion powder, salt, and black pepper in a large bowl. Mix thoroughly until well combined.
Add the pork belly to the marinade, ensuring it's completely coated. Cover and refrigerate for at least 3 hours (overnight for best results).
Preheat your grill to medium-high heat.
Grill the marinated pork belly until thoroughly cooked, about 15-20 minutes, turning occasionally to ensure even cooking. Check that there's no pink in the center.
Let the pork rest for 5 minutes, then slice into bite-sized serving pieces.
Make the sauce by combining white vinegar, soy sauce, white sugar, salt, and ground black pepper in a large mixing bowl. Stir until the sugar dissolves.
Add the sliced pork, cucumber, tomato, red onion, and chili pepper to the sauce.
Toss everything together until well coated with the vinegar sauce.
Transfer to a serving plate and enjoy!