SPRINKLE both sides of each chicken breast with garlic powder.
HEAT oil in Dutch oven or large saucepot on medium-high heat. Add chicken; cook 1 to 2 min. on each side or until browned on both sides. Remove from pan; set aside. Add water to pan. Bring to boil. Stir in Shell Macaroni; top with chicken. Cover; simmer on medium-low heat 12 min. or until shells are tender.
STIR in tomato and Cheese Sauce. Cook on medium-low heat 2 to 3 min. or until cheese sauce is melted and mixture is heated through, stirring occasionally.