Cook pasta according to directions on packet, drain.
Heat oil in pan, add onion, cook 2 minutes. Add ham and combined CARNATION Creamy Evaporated Milk, water and cornflour, bring to boil stirring. Add half the cheese and pasta, mix to combine.
Spoon mixture into an ovenproof dish. Top with tomato, sprinkle with combined breadcrumbs and remaining cheese. Place under hot grill until golden brown.