First, prepare the mango guacamole by mashing the avocado and then mixing it with cilantro, lime juice, salt, and mango chunks. Set aside.
Next, prepare the ahi tuna marinade. Combine the soy sauce, red chili sauce, grated ginger, and lime juice in a medium container. Add in the ahi tuna steaks and make sure to dip both sides. Let sit in the fridge for 30 minutes.
Remove ahi tuna steaks from the refrigerator and then remove from the marinade. Pour sesame seeds on a plate and coat every part of both tuna steak with sesame seeds
Heat a large skillet over medium/high heat and 2 tablespoons of olive oil. When the olive oil is fragrant, add one tuna steak to the pan and sear for 30 seconds to 2 minutes on each side.*
When ahi tuna steak is cooked, carefully slice the ahi tuna into thin strips.
Prepare the tacos by equally distributing tuna, cilantro, and red onion into tortillas. Then, top with 1-2 tablespoons of mango guacamole.