Start by patting the pork belly slab dry with paper towels. Score the skin with a sharp knife, making shallow cuts about 1 inch apart. This helps the skin crisp up during grilling. Season the meat side generously with salt, pepper, and your choice of dry rub or marinade. Allow the pork belly to sit at room temperature for about 15 minutes before grilling.
Preheat your grill to medium heat. If using a charcoal grill, light the charcoal and let it burn until covered with white ash. If using a gas grill, preheat it to medium heat. For an added smoky flavor, you can add soaked wood chips or chunks to the charcoal or use a smoker box with gas grills.
Place the pork belly slab on the grill, skin side down. Close the lid and let it cook for about 10-15 minutes to allow the skin to start crisping up. Afterward, flip the pork belly, skin side up, and continue grilling with the lid closed. If using a gas grill, turn off the burners directly underneath the pork belly and keep the other burners on.
Insert a meat thermometer into the thickest part of the pork belly, avoiding contact with the bone. Continue grilling until the internal temperature reaches 190°F (88°C). This will ensure that the meat is tender and the fat has rendered.
Once the pork belly reaches the desired internal temperature, you can increase the heat or move it closer to the heat source to crisp up the skin. Keep a close eye on it to prevent burning. Allow the skin to turn crispy and golden brown, which usually takes an additional 5-10 minutes.
Remove the pork belly from the grill and let it rest for about 10 minutes. This allows the juices to redistribute and ensures a tender and juicy final product. Slice the grilled pork belly into desired portions and serve.