How to Make It
Marinade: Whisk together olive oil, garlic cloves, lemon zest and juice, chopped thyme, salt, and black pepper in a small bowl. Place chicken cutlets in a 1-gallon zip-top plastic freezer bag, and add marinade. Seal bag, and turn to coat. Chill 30 minutes to 1 hour, turning occasionally. Remove chicken from bag and marinade; discard marinade.
Dressing: Whisk together buttermilk, mayonnaise, chives, lemon juice, pressed garlic clove, thyme, salt, and black pepper in a small bowl; cover and chill.
Couscous: Cook couscous and lemon peel strips in heated olive oil in a medium saucepan over medium, stirring often, until mostly golden, 7 to 8 minutes. Add water and salt; bring to a boil. Cover, reduce heat to low, and simmer until barely tender, 8 to 10 minutes. Drain and discard lemon peel strips.
Chicken and vegetables: Coat cold cooking grate of grill with cooking spray, and place on grill. Preheat grill to medium (350° to 400°). Toss asparagus with 1 tablespoon olive oil, and sprinkle with salt and black pepper. Brush both sides of onion slices with remaining olive oil. Grill chicken, asparagus, and onions until chicken is done and vegetables are tender and charred, about 3 minutes on each side.
Slice chicken; cut asparagus into 2-inch pieces, and roughly chop onions. Toss together couscous, chicken, asparagus, onions, and 1/2 cup dressing. Serve salad with remaining dressing.