PREHEAT oven to 350°F. Mix chicken, celery, 1/2 cup of the cheese, dressing, onion, lemon juice and seasonings until well blended.
SPOON into 1-1/2-quart casserole dish; top with tomatoes.
BAKE 35 minutes; top with combined remaining 1/2 cup cheese and chips. Bake an additional 5 minutes or until cheese is melted.