Toss chicken with pesto in medium bowl. Cook chicken mixture in large nonstick skillet over medium-high heat, stirring frequently, until chicken is almost cooked, about 5 minutes. Stir in mushrooms and tomatoes. Cook, stirring occasionally, 5 minutes or until chicken is thoroughly cooked. Toss with Knorr® Sidekicks® Fettuccine Alfredo Pasta Side Dish.