Add broth, lemon juice and lemon slices to same skillet. Heat to boiling over high heat. Cook, stirring constantly, until broth is reduced by half. Return chicken to skillet; cook 1 to 2 minutes to glaze. Remove lemon slices from skillet; discard. Spoon couscous onto serving plates; top with tomato slices. Place chicken over tomato; drizzle with juices in skillet.