Pesto: Place the basil, pine nuts, cheese, lemon juice, lemon zest, garlic, salt and pepper in a food processor; pulse until finely chopped. With the motor running, slowly add the oil until well combined.
Salad: Preheat the grill to medium-high; lightly coat the grate with cooking oil. Whisk the olive oil with the vinegar, garlic, salt and pepper. Toss some of the mixture with the red pepper, zucchini and onion. Brush the remaining mixture all over chicken. Grill the chicken and vegetables, turning as needed, for 10 to 15 minutes or until cooked though and well-marked. Cool completely. Thinly slice the chicken and chop the vegetables. Toss the couscous with the chopped vegetables and 1/3 cup pesto. Divide evenly between 4 plates and top with sliced chicken. Drizzle each salad with 1 tbsp additional pesto. Left over pesto can be stored in a tightly covered container for up to 5 days.
Toast pine nuts at 350°F, in a single layer, for 7 to 10 minutes or until golden and fragrant. For extra flavor, cook the couscous in chicken broth.