1. Combine egg whites, milk and herbs in a small bowl. Season with pepper.
2. Coat a small nonstick skillet with cooking spray.
3. Heat the skillet on medium to low heat.
4. Add chopped spinach. As it wilts, pour egg white mixture over the spinach and allow to set around the edges.
5. As the edges set, lift them gently with a spatula and tip the skillet to allow remaining liquid underneath.
6. When the egg whites are set, sprinkle the cheese on top, then fold the omelet in half. Serve immediately.