If using wooden skewers, soak them in water for at least 30 minutes before threading.
Cut pork tenderloin, pineapple, red onion, and green bell pepper into even 1-inch pieces.
In a small bowl, whisk together the BBQ sauce, olive oil, soy sauce, garlic powder, and black pepper until well combined.
Place the pork, pineapple, onion, and bell pepper in a large bowl. Pour the BBQ sauce mixture over everything and toss to coat evenly.
Thread the marinated pork, pineapple, and vegetables onto skewers, alternating ingredients as you go.
Preheat your grill to medium heat. Place the skewers on the grill grates.
Grill for 15 to 20 minutes, turning the skewers every few minutes, until the pork is cooked through (internal temperature of 145°F / 63°C) and the vegetables are tender with grill marks.
In the last 3 to 4 minutes of grilling, brush the skewers with additional BBQ sauce for a caramelized glaze.
Remove from the grill and rest for 2 minutes before serving.