In a mixing bowl, whisk together egg, egg whites, herbs, salt and pepper until fully combined and frothy, 30 seconds to 1 minute.
Coat an 8-inch nonstick skillet with cooking spray; add butter. Heat over medium heat until butter melts; swirl pan to distribute butter. Add egg mixture; tilt pan to distribute egg. As eggs solidify, push them gently into center of pan; tilt pan to allow any uncooked eggs to fill open space around edges. Cook until there is no liquid remaining, about 1-2 minutes. Reduce heat slightly; cook until eggs are set, 30 seconds-1 minute. (If you prefer your eggs more fully cooked, cover pan for last minute.)
Loosen omelet edges with a spatula, slide omelet onto a plate, fold over and serve.