Pour into 8-inch nonstick skillet sprayed with cooking spray; cover. Cook on medium heat 6 min. or until egg mixture is set but top is still slightly moist, occasionally lifting edge with spatula and tilting skillet to allow uncooked portion to flow underneath. Sprinkle cheese onto half the omelette. Slip spatula underneath omelette, tip skillet to loosen and gently fold omelette in half. Remove from heat; let stand, covered, 2 min.