Trim any excess fat from the chicken thighs and pat them dry with paper towels.
Rub the chicken thighs with olive oil to help the spices adhere.
Season the thighs with kosher salt, black pepper, and garlic powder. Let them sit at room temperature while you prepare the marinade.
In a large bowl, combine the harissa paste, honey, fresh lemon juice, olive oil, minced garlic, ground cumin, smoked paprika, ground coriander, and ground cinnamon.
Mix well until the marinade is smooth and well-blended.
Place the chicken thighs in a large resealable plastic bag or a shallow dish.
Pour the harissa honey marinade over the chicken thighs, ensuring they are well-coated. Seal the bag or cover the dish and refrigerate for at least 2 hours, or overnight for best results.
Preheat your grill to medium-high heat (about 375-400°F).
Oil the grill grates to prevent sticking.
Remove the chicken thighs from the marinade, letting any excess drip off. Discard the marinade.
Place the chicken thighs on the grill, skin-side down. Grill for about 5-7 minutes, or until the skin is crispy and has nice grill marks.
Flip the chicken thighs and move to indirect heat. Close the lid and continue cooking for another 20-25 minutes, or until the internal temperature reaches 165°F.
Brush the chicken thighs with any remaining marinade during the last 5 minutes of grilling.
Once the chicken thighs are done, remove them from the grill and let them rest for about 5 minutes.