Heat a skillet to medium-high heat. Rub tuna steaks on both sides with salt, pepper and Asian seasoning. Rub tuna steaks lightly with oil. (Don't oil the pan!).
Place the steaks in the skillet and cook, without touching, for 2-3 minutes or until the tuna looks cooked and white about halfway up it's side. Drizzle the upside of the steak lightly with more oil and flip. Do not touch for another 2 minutes. The outside of the steaks will be seared, but the insides should remain pink. (It is safe to eat most tuna steaks rare in the middle. As always, do an eye and sniff test to be sure. I bought mine at Kroger and had no issue).
Remove steaks from pan and immediately drizzle with about 1 teaspoon olive oil and the lemon juice. This will prevent dryness. Let sit for a few minutes, then slice into strips.
To make the cilantro wasabi mayo, mix all mayo ingredients together in a bowl. Taste and adjust to your liking.
Assemble the tacos with the tuna, cabbage, avocado, mango and mayo. Top with additional cilantro for garnish.