In a cast-iron skillet over medium heat, lightly toast the chiles, about 2 to 3 minutes on each side. Remove from the skillet and set aside.

In the same skillet, add the onion and garlic, turning ,once or twice until they are lightly charred, about 10 minutes. Remove from the skillet and set aside. 

Add the peppercorns, clove, and dried oregano to t l pan and lightly toast until they are aromatic, about 2 minutes. Transfer the toasted spices and oregano to a molcajete or spice grinder and grind until finely ground.

In a high-performance blender or food processor, add the toasted chiles, onion, garlic, ground spices and oregano, oil, orange juice, rice vinegar, lime juice, cinnamon, and salt. Blend until most of the chiles I come apart.

Pat the chicken dry with paper towels. Using a gallon-size resealable bag, add the marinade and the chic Seal and let sit in the refrigerator for at least 30 minutes or overnight.

Remove the chicken thighs in their marinade from the fridge to allow them to reach room temperature before grilling.

Start a charcoal or gas grill. The gas should be set high. If using a pellet grill, preheat your grill to 450ºF for at least 15 minutes. If using charcoal, the coals should be red but entirely covered with gray ash.

Remove the chicken from the marinade and put them on the grill directly over the medium fire, skin side up. Close the lid and cook, turning once, about 15 minutes on each side. The chicken is cooked when its internal temperature reaches 175°F  on a meat thermometer. Transfer the meat to a cutting board and let rest for 5 minutes.