Add to skillet; cook 2 to 3 min. or until eggs are almost set, lifting edge with spatula and tilting skillet to allow uncooked portion to flow underneath. When egg mixture is set but top is still slightly moist top with cheese. Slip spatula underneath omelette, tip skillet to loosen and gently fold omelette in half. Cook 1 to 2 min. Slide or flip onto serving plate. Serve with tomato slices.