Make the seasoning rub. In a small bowl or glass measuring cup, add the olive oil, red wine vinegar, tomato paste, garlic, and spices. Whisk to combine.
Pat the chicken dry and season with kosher salt and black pepper on both side. Pour about ¾ of the rub you just made all over the chicken (reserve the rest for later) and toss to make sure all the pieces are well coated. Set aside for now.
Put the vegetables and onions in a mixing bowl. Season with kosher salt and black pepper and pour the remaining seasoning rub. Toss to combine.
Transfer the chicken and vegetables to a large baking pan or rimmed sheet pan.
Bake in the center of the heated-oven for 40 to 45 minutes or until the chicken is fully cooked and the juices run clear. The vegetables should also soften and gain some char.
While the chicken and veggies are baking, prepare the couscous. Boil the water or both until bubbling. Heat a tablespoon of olive oil in a saucepan. Add the couscous and cook, tossing regularly, until the couscous is toasted to golden brown. Season with kosher salt and ½ teaspoon ground cinnamon. Add the boiled water. Immediately turn the heat off and cover the saucepan. Leave the couscous undisturbed for 10 minutes, the couscous should absorb all the liquid. When ready, add the fresh parsley and fluff the couscous with a fork.
When the chicken is fully cooked through, remove it from the oven. Spoon the couscous between the chicken pieces and allow it about 5 minutes to sop up some of the pan juices. Finish with the raisins, if you like.
Prepare ahead: You can season and marinate the chicken in the fridge a few hours or up to 1 night in advance.
Leftover chicken couscous can be stored in an airtight container in the fridge for 3 to 4 days. Reheat on the stovetop over medium heat just until the chicken has warmed through (you may add a little liquid if needed).