Place a skillet over medium-high heat and spray with nonstick cooking spray. Add ham and cook until lightly browned.
Remove ham from the skillet and set aside.
Wipe out skillet and spray with nonstick cooking spray.
Pour egg whites into the skillet, tilt to cover the bottom of the pan in an even layer and cover with a lid for 3-5 minutes, or until eggs are set.
Remove lid and top half of the omelet with ham and cheese.
Use a rubber spatula to lift the edges of the omelet and fold in half.
Carefully slide the omelet onto a plate and serve.