In a large nonstick skillet, heat EVOO over medium-high. Add mushrooms and rosemary; season. Cook until mushrooms are soft, about 5 minutes. Transfer to a bowl; cover. In another bowl, whisk eggs, 1 tbsp. cold water and a pinch salt. Lightly coat the skillet with cooking spray; heat over medium. Add eggs and cook, tilting pan and lifting omelet edges as needed, until set, about 3 minutes. Sprinkle half the omelet with cheese, then mushrooms. Fold in half to enclose filling and slide onto a plate. Garnish with more rosemary, if desired.
