These tacos are a great way to finish off the last of a batch of Yellowfin. With big hunks of juicy tuna, redolent of garlic and cilantro and the bold flavors of warm spices like cumin, coriander and oregano, it's a light yet satisfying summer meal. Since you don't need to marinate tuna for very long, this makes for a great weeknight meal. Because Yellowfin tuna is very lean, it's important not to overcook it as it will end up tough and dry. That's why this recipe works best if the skewers are seared on two sides using a very hot cast iron grill pan or skillet rather than using a conventional grill.