Preheat oven to 400 degrees. Place whole bell pepper on a baking sheet and cook for 25 minutes or until skin blackens and flesh is tender. Remove from the oven and slip into a small paper bag. Roll up the end of the bag and let the pepper steam.
In a small skillet toast the coriander, cumin and caraway seeds until fragrant, and beginning to sizzle and pop, about 3-4 minutes. Transfer to a mortar and pestle or spice grinder and grind or pulse to a powder.
Heat the oil in a frying pan over medium heat and add the onion, garlic and fresh chilies. Cook 6-8 minutes until fragrant and slightly browned.
Peel the skin and remove the seeds from the bell pepper. Add the bell pepper flesh to a blender. Add the spices, the onion mixture, red pepper flakes, lemon juice and zest, tomato paste and salt.
Pulse until well combined. Pour the mixture into a bowl and add the Greek yogurt and stir.
Place the chicken thighs in a gallon zip-top baggie. Add the harissa mixture. Squeeze most of the air out of the baggie and seal it. Work the harissa and chicken together until the thighs are well coated. Refrigerate overnight.
Preheat the oven to 425.
Place the chicken thighs, well spaced, on a large baking sheet. Scatter the onion pieces over and around the chicken. Top each chicken thigh with a slice of the lemon and roast for 5 minutes. Reduce the oven temperature to 350 and cook for another 12-15 minutes, until the chicken is almost cooked. Then, place it under the broiler for 2-3 minutes to give it extra color and cook it through completely. Sprinkle with fresh cilantro just before serving.
elicious with jasmine rice, couscous or crispy roasted potatoes.