- Wash and pat dry tuna with kitchen towel/paper.  
- Prepare two medium bowls: one with soy sauce, sesame oil and the other with mixed black and white sesame seeds. 
- Add the tuna to the marinade first, make sure it is coated on all sides. Let marinate for 10-20 minutes. Dip the tuna into sesame seeds until all the sides are covered. You may need to press the seeds into the tuna to make sure they stick nicely.  
- Place a pan over medium heat and add enough oil. 
- Once the oil is hot add tuna steak and sear for 2 minutes on one side. Flip the tuna and sear the other side for another 2-3 minutes. Important to note that the cooking time will depend on the thickness of the tuna steak. Mine was about 1 ½ inches thick. Place a good nonstick skillet/pan over medium heat and add enough oil.  
- For more traditional 4-6 ounces and 1 ½ inches thick tuna steak. Sear for 1 ½ minutes on one side, flip and sear another 1 - 1 ½ minutes. Orr use a thermometer to register 118-120 Fahrenheit in the center for medium-rare (that's what i did). 
- Allow resting on a plate for 1-2 minutes. Once it's cooled more it will be easier to cut it into even slices. Season with sea salt and black pepper. 
- Ahi tuna is ideally served medium-rare but if you prefer your tuna more cooked, add another 1-2 minutes per side. Just make sure not to overcook it, it should still be pink inside. 
- If not sure, take it off the pan, cut in the middle, and see if it is cooked to your liking, if not just sear it for a couple of minutes longer. You only need a minute or two here for a medium-rare tuna steak. If all the pink is disappeared, the tuna is still edible but will be more on the dryer side. 
- Important to note here: different burners will give different results but use your best judgment and always aim for ''not overcooking'' the tuna steak. In this case, you can still fix the situation. 
- Once you start cutting it up into slices and see that the steak seems too raw for you, just pop it back into the hot pan and cook for a minute or so. But if overcooked there's nothing you can do anymore. 
- Meanwhile, warm up your tortillas on a hot dry pan until golden brown or heat in the oven. Or on the grill! 
- Assemble. In warmed taco shell add a handful of shredded cabbage, 1-2 tablespoons of Mango Habanero Salsa, and top with or two slices of fish. 
- Drizzle with fresh lime juice, fresh black cracked pepper, and sea salt flakes, and serve these mouthwatering seared ahi tuna tacos immediately.