In a large bowl, combine the teriyaki sauce, soy sauce, rice vinegar, brown sugar, garlic powder, ground ginger, and black pepper. Whisk until the sugar is dissolved. Add the chicken thighs, ensuring they are well-coated. Let it marinate for at least 15 minutes (or up to 2 hours in the fridge for more flavor).

In a medium bowl, mix diced pineapple, red bell pepper, red onion, cilantro, jalapeño (if using), lime juice, and season with salt and pepper. Set aside to allow the flavors to meld.

Preheat your grill or grill pan over medium-high heat. You want it hot enough that the chicken will sizzle when it hits the grill. If using a grill pan, lightly oil it to prevent sticking.

Remove the chicken from the marinade (discard the marinade) and place the thighs on the grill. Cook for 5-7 minutes on one side without moving, until grill marks appear and the chicken releases easily.

Flip the chicken and cook for another 5-7 minutes, or until the internal temperature reaches 165°F (75°C).

Once cooked, remove the chicken from the grill and let it rest for about 5 minutes.

While the chicken is resting, warm the tortillas on the grill for 1-2 minutes per side until soft and pliable.

Slice the grilled chicken into strips. Assemble the tacos by placing a layer of shredded cabbage on each tortilla, followed by the chicken slices and topping with the pineapple salsa.

Serve with lime wedges and extra cilantro for garnish. Enjoy your tacos fresh!