Lay pork belly slab on cutting board, skin-side down. Use sharp knife to make vertical cuts from top edge of pork belly to bottom edge of pork belly. Cuts should be 1-inch apart and only cut ⅔ through slab of pork belly. Do not cut through pork belly completely. Set pork belly aside.
Open sealable food-safe bag and pour in soy sauce, honey, lime juice, and chili paste if using.
Place pork belly slab in bag with marinade. Seal bag almost completely, then squeeze out as much air as possible. Finish sealing bag and place bag in refrigerator. Chill at least 1 hour, but no more than 8 hours.
Preheat grill to medium heat, approximately 350° to 375° Fahrenheit. Remove pork belly slab from bag and place on grill grate over direct heat. Transfer remaining marinade to medium bowl and keep close by.
Close grill lid and cook pork belly 3 minutes. At 3 minutes, open lid and carefully flip pork belly over. Brush marinade over top of pork belly and close lid. Repeat process, flipping and basting pork belly every 3 minutes, until pork belly is fully cooked - approximately 20 minutes.
Remove fully cooked pork belly from grill and place on cutting board. Let pork rest 5 minutes, then finish slicing original cuts through completely, leaving you with vertical strips for serving. Serve warm with desired sides.