1.Preheat oven to 175°C (350°F).
2.Cut each tomato into eight wedges. Combine tomato, in single layer, with garlic and half of the oil in large shallow casserole; roast, uncovered, 30 minutes.
3.Meanwhile, heat remaining oil in large nonstick skillet; cook chicken, in batches, until lightly browned all over.
4.Place vinegar, honey, sherry and mustard in same skillet; bring to a boil. Return chicken to skillet; reduce heat. Simmer, uncovered, 10 minutes or until chicken is cooked through.
5.Bring water to a boil in medium saucepan; stir in couscous and butter. Remove from heat; let stand, covered, 5 minutes or until liquid is absorbed, fluffing with fork occasionally. Stir in tomato mixture and basil; toss with fork to combine.
6.Serve chicken on couscous; drizzle with remaining pan juices.