In a mixing bowl, combine the ancho chili powder, achiote paste, ground cumin, minced garlic, chopped chipotle peppers in adobo sauce, kosher salt, smoked paprika, ground cinnamon, orange juice, apple cider vinegar, and brown sugar. Whisk until everything is well-combined. Each ingredient plays a crucial role in developing the profound flavor that defines your tacos.

Place the boneless chicken thighs in a large resealable plastic bag. Pour the marinade over the chicken, ensuring it's completely coated. Add the finely chopped pineapple and yellow onion to the bag. Seal it tightly, then shake and massage the bag to spread the marinade evenly. Refrigerate for at least one hour—preferably overnight for maximum flavor impartation.

Preheat your grill to medium-high heat. Remove the chicken from the marinade and discard the excess marinade. Grill the chicken thighs for approximately 6-8 minutes per side or until they reach an internal temperature of 165°F. This will give them a lovely char and smoky flavor.

Once cooked, transfer the chicken to a cutting board and cover it with foil. Let it rest for about 5-10 minutes. Resting the chicken allows the juices to redistribute, ensuring tender meat. After resting, chop the chicken into bite-sized pieces.

Warm your corn tortillas on the grill or a hot skillet for about 30 seconds per side. This will make them pliable and enhance their flavor. A good tortilla is the genuine essence of a great taco.

Spoon the chopped chicken onto each warm tortilla. Top with your choice of toppings—cilantro, pickled onions, salsa, lime juice, or queso fresco. The beauty of this dish is in its adaptability. Enjoy right away!