Cook couscous according to package directions; remove from heat. Meanwhile, in a large bowl, whisk lemon juice, oil, mustard, garlic, salt and pepper until blended; stir in 1/4 cup basil. Stir 1/4 cup dressing into cooked couscous; reserve remaining dressing.
Thread shrimp onto metal or soaked wooden skewers. Grill shrimp, covered, on an oiled rack over medium-high heat until pink, 2-3 minutes on each side.
Remove shrimp from skewers; toss with reserved dressing. Serve with couscous. Sprinkle with lemon zest and remaining basil.
