Combine harissa spice blend, lemon juice, olive oil, and garlic in a small bowl. Rub spice mixture over chicken thighs, including under the skin. Refrigerate for 1 to 4 hours. Remove from refrigerator 20 minutes before grilling.

Preheat an outdoor grill for medium-high heat, and lightly oil grate.

Place chicken thighs on the hot grill, skin side down, and grill for 3 to 4 minutes. Flip the chicken over and grill on the other side for 3 to 4 minutes. Continue flipping every 3 to 4 minutes until the internal temperature reaches 165ºF, about 20 to 25 minutes total. Remove chicken to a plate and cover with foil; let rest for 5 minutes.

Meanwhile, combine harissa seasoning, honey, and melted butter for glaze in a small microwave-safe bowl. Microwave until mixture is heated through and has a thinned consistency, about 10 seconds. Drizzle over chicken and serve.