Beat egg whites in large bowl until soft peaks form.
Beat egg yolks with mayonnaise and 2 tablespoons water in separate bowl.
Place butter in 9-inch microproof pie plate.
Cook on HI, 30 seconds, or until butter melts.
Tilt pie plate to coat evenly with butter.
Pour egg mixture into pie plate.
Cook on 60, 6 to 8 minutes.
Rotate dish if eggs seem to be rising unevenly.
When eggs are set but still moist, sprinkle with cheese.
Cook on 60, 1 minute, or until cheese melts.
Fold omelet in half and slide onto serving plate.
Sprinkle with parsley.