In a large mixing bowl, combine soy sauce, minced garlic, brown sugar, and black pepper. Stir in calamansi juice and vegetable oil until the sugar dissolves.

Cut pork shoulder butt into bite-sized cubes and add to the marinade. Ensure each piece is thoroughly coated. Cover and refrigerate for at least 3 hours or overnight.

Preheat your grill to medium-high heat (about 400°F). Soak wooden skewers in water for at least 15 minutes to prevent burning.

Thread marinated pork onto soaked skewers, leaving space between each piece. Add bell peppers and onions if using.

Grill skewers for 3-5 minutes per side until nicely browned and caramelized, ensuring an internal temperature of at least 145°F.

After grilling, let the skewers rest for about 5 minutes before serving with a spicy dipping sauce.