In a large bowl, combine pineapple juice, soy sauce, brown sugar, garlic, ginger, sesame oil, and black pepper. Add the chicken thighs, ensuring they are well coated. Cover and marinate in the refrigerator for at least 1 hour, or up to overnight for more flavor.
Preheat your grill or a large skillet over medium-high heat. Add vegetable oil to the skillet if using.
Remove the chicken from the marinade, letting excess liquid drip off. Grill or cook in the skillet for about 6-7 minutes per side, or until the chicken is cooked through and has a nice char.
Once cooked, let the chicken rest for 5 minutes before slicing it into strips.
Warm the flour tortillas on the grill or in a dry skillet for about 30 seconds on each side.
Assemble the tacos by placing a few strips of chicken on each tortilla. Top with shredded cabbage, diced tomatoes, green onions, and cilantro.
Serve with lime wedges on the side for squeezing over the tacos.