In a small bowl, whisk together the paprika, cumin, 1 teaspoon salt, ¾ teaspoon pepper, turmeric, cayenne, cinnamon, and ginger.
In a food processor, pulse the olive oil, prunes, olives, garlic, and spice mixture until smooth paste forms, about 1 minute, scraping down sides of bowl as needed. Transfer the paste to a large bowl with the chicken thighs and toss to coat them well. Cover and refrigerate for at least 30 minutes and up to 1 day.
On a gas grill, turn all burners to medium-high, cover, and heat until hot, about 15 minutes. Once hot, oil your cooking grates. Arrange chicken on the grill. Cover and cook for 10 minutes, flip over, and cook for an additional 6 to 8 minutes, until the chicken registers 185 degrees on an instant-read thermometer. Transfer the chicken thighs to a platter, tent with aluminum foil, and let rest for 10 minutes.
While the chicken is grilling, make the couscous: In a medium saucepan, bring the broth, salt, and oil to a boil. Stir in the couscous, cover tightly with a lid, and remove from heat. Let the couscous stand for 5 minutes. Use a fork to fluff the couscous and stir in the lemon juice, parsley, prunes, olives, and pecans. Taste and adjust seasoning with salt and pepper as desired.
Arrange the couscous on a large platter, top with the cooked chicken thighs, and serve with lemon wedges, if desired.