Lightly coat an unheated 6- to 7-inch nonstick skillet with flared sides with nonstick cooking spray. Preheat skillet over medium heat. Add mushrooms, green onion, and garlic to skillet; cook until tender; stirring frequently. Remove mushroom mixture from skillet using a slotted spoon; set aside. If necessary, pour liquid out of skillet; carefully wipe out skillet.
In a medium bowl, combine egg product or eggs, herbes de Provence, salt, and pepper. Beat with a whisk or rotary beater until combined. Add 1/2 teaspoon of the oil to clean skillet. Preheat skillet over medium heat.
Pour half of the egg mixture into prepared skillet. Cook, without stirring, about 1 minute or until egg mixture begins to set. Run a spatula around edge of skillet, lifting egg mixture so uncooked portion flows underneath.
Continue cooking and lifting edges until egg mixture is set but is still glossy and moist. Sprinkle with half of the mozzarella cheese. Top with half of the mushroom mixture. Continue cooking until cheese just begins to melt. Using the spatula, lift and fold an edge of the omelet partially over filling. Transfer omelet to a warm plate. Prepare another omelet with remaining oil, egg mixture, mozzarella, and mushroom mixture. Top omelets with Asiago or Parmesan cheese, tomato, and, if desired, parsley.
Spray the cold skillet with cooking spray instead of cooking the vegetables with oil or butter.