Combine barbecue sauce, pineapple juice, garlic, salt, and fresh ground pepper in a bowl; whisk until thoroughly incorporated.
Combine cut up pork, pineapples, peppers, and onions in a mixing bowl; season with adobo seasoning, salt, and pepper, and toss to combine.
Preheat grill to medium-high.
Thread pork onto skewers, alternating with onions, pineapples, and peppers.
Reserve 1/2 cup prepared barbecue sauce for serving; brush skewers with remaining barbecue sauce.
Grill skewers for 8 to 10 minutes, turning occasionally, or until pork is thoroughly cooked and vegetables are tender and charred.
Transfer to a platter and brush lightly with barbecue sauce.
Serve with remaining barbecue sauce on the side.