Preheat the broiler. Cook the couscous according to package directions. Let cool.
Thread the chicken and peppers onto 8 skewers. In a bowl, mix 1 tbsp. oil and 1 1/2 tsp. vinegar; brush on skewers. Sprinkle with Italian seasoning. Broil, turning once, until the chicken is cooked, about 6 minutes.
In a bowl, toss the spinach, onion, prunes, couscous and the remaining 2 tbsp. olive oil and 1 tbsp. vinegar. Serve with the skewers.