In a mixing bowl, combine soy sauce, sesame oil, honey, minced garlic, grated ginger, lime juice, and red pepper flakes to create the marinade.
Place the Ahi tuna steaks in a ziplock bag or airtight container and pour the marinade over them, ensuring they are evenly coated. Marinate in the refrigerator for at least 30 minutes, allowing the flavors to infuse into the fish.
Preheat your grill to high heat. Clean the grates using a grill brush to prevent sticking.
Take out the tuna steaks from the marinade and dispose of the marinade.
Season the tuna steaks with salt and pepper.
Place the tuna steaks on the hot grill and sear for about 2-3 minutes per side, depending on the desired level of doneness. For medium-rare, cook 2 minutes per side. For medium, cook 3 minutes per side.
Once done, remove the tuna from the grill and let it rest for a minute before slicing.
Garnish with fresh cilantro leaves and serve hot.