Preheat oven to 400F and lightly grease a large sheet pan. Toss sweet potatoes, onion, chickpeas, 2 tablespoons harissa, 2 tablespoons olive oil, salt, and pepper to taste together and arrange in a single layer.
Roast vegetables at 400F 20-25 minutes until sweet potatoes are crisp-tender. Remove from oven and keep oven on.
Season chicken on both sides with salt and pepper to taste. Heat butter and remaining 1 tablespoon olive oil in a large skillet over medium-high heat until melted and hot. Place chicken thighs skin-side down and sear 3-5 minutes on both sides until golden brown.
Remove chicken from skillet and arrange on sheet pan with vegetables. Set aside for a moment.
In a small bowl, mix remaining 1/4 cup harissa with lime juice and honey until smooth and season with salt to taste. Use a spoon to spread harissa sauce over chicken thighs.
Roast chicken and vegetables at 400F 15-20 minutes until chicken registers 165F and vegetables are tender. Serve chicken and vegetables warm with fresh lime wedges and additional cilantro on top. Enjoy!