Preparing the Tuna Steaks

1. Pat the tuna steaks dry and season both sides liberally with salt, pepper, and the Asian seasoning blend.
2. Lightly brush each side of the seasoned tuna steaks with olive oil.
3. Heat a skillet over medium-high heat until hot.
4. Place the tuna steaks into the skillet and let them cook undisturbed for about 2-3 minutes until you notice they are cooked about halfway up the sides.
5. Lightly drizzle the uncooked side with a bit of olive oil and then carefully flip the steaks to sear the other side.
6. Let them cook for an additional 2 minutes. The steaks should be nicely seared on the outside but remain pink in the middle.
7. Once done, transfer the steaks to a plate.
8. Drizzle them with approximately 1 teaspoon of olive oil and the lemon juice to maintain moisture.
9. Let the steaks rest for a few minutes before slicing them into thin strips.

Making the Cilantro-Wasabi Mayo

1. In a mixing bowl, combine the mayonnaise, wasabi paste, lemon juice, and chopped cilantro.
2. Season with salt and pepper.
3. Mix well and taste the mayo. Adjust the seasoning if required.

Assembling the Tacos

1. Start with placing a layer of shredded cabbage on each taco shell.
2. Add the sliced tuna, avocado slices, and mango slices on top of the cabbage.
3. Drizzle a generous amount of the cilantro-wasabi mayo over the fillings.
4. Finish off with some freshly chopped cilantro on top for added flavor and garnish.
5. Serve immediately.