Combine all marinade ingredients in a bowl until throughly mixed. Season with salt and pepper to taste.
After thoroughly rinsing and clean the tuna jaw, place it in a separate bowl or sealable bag and pour the marinade mixture until the jaw is fully submerged and coated.
Place in the refrigerator to marinade at least 2 hours and up to overnight.
When ready to cook, combine the basting/serving sauce and set aside.
Cook the tuna jaw on a grill or pan over high heat, while liberally basting the sauce over the fish.
Let it cook for 3 to 5 minutes and flip to cook the other side. Cook for another 3 to
5 minutes, making sure to thoroughly brush the sauce over the entire fish.
Once fully cooked, allow the fish to rest for a few minutes before serving.
Optionally, you can warm the basting sauce until the sugar is fully dissolved. This can be served alongside the fish as a dipping sauce.
Garnish with calamansi and your condiments of choice!