Combine Worcestershire, garlic, ketchup, lemon juice, black pepper and sea salt in a large bowl. Mix well.
Place pork belly in the bowl. Mix to coat with the marinade.
Place pork belly and marinade in a ziptop bag. Store in the fridge overnight.
Preheat grill over medium heat.
In a small bowl, combine leftover marinade, ketchup and oil. Whisk well. This will be used as a basting sauce for the pork belly.
Place pork belly side by side on the grill. Make sure they do not overlap. Cook for 1-2 minutes. Keep an eye on it as the pork cooks.
Flip to cook the other side. Baste and grill for 1-2 minutes.
Flip again and baste. Continue to grill until cooked.
Chop and serve.